U.S. patent application number 15/112033 was filed with the patent office on 2016-11-24 for compositions comprising an oxidizer and water, compositions comprising biomass, a biomass-oxidizer, and water, and methods of making and using the same.
The applicant listed for this patent is GEORGIA TECH RESEARCH CORPORATION. Invention is credited to Yulin DENG, Wei LIU, Wei MU.
Application Number | 20160344055 15/112033 |
Document ID | / |
Family ID | 53543525 |
Filed Date | 2016-11-24 |
United States Patent
Application |
20160344055 |
Kind Code |
A1 |
DENG; Yulin ; et
al. |
November 24, 2016 |
COMPOSITIONS COMPRISING AN OXIDIZER AND WATER, COMPOSITIONS
COMPRISING BIOMASS, A BIOMASS-OXIDIZER, AND WATER, AND METHODS OF
MAKING AND USING THE SAME
Abstract
Disclosed herein are compositions comprising an oxidizer, water,
and optionally a neutralizer, and methods of making and using the
same. Also disclosed herein are compositions comprising biomass, a
biomass-oxidizer, water, and optionally an accelerant, and methods
of making and using the same.
Inventors: |
DENG; Yulin; (Atlanta,
GA) ; LIU; Wei; (Atlanta, GA) ; MU; Wei;
(Atlanta, GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GEORGIA TECH RESEARCH CORPORATION |
Atlanta |
GA |
US |
|
|
Family ID: |
53543525 |
Appl. No.: |
15/112033 |
Filed: |
January 17, 2015 |
PCT Filed: |
January 17, 2015 |
PCT NO: |
PCT/US2015/011881 |
371 Date: |
July 15, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61928760 |
Jan 17, 2014 |
|
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|
62051443 |
Sep 17, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02E 60/527 20130101;
Y02E 70/20 20130101; H01M 4/9016 20130101; H01M 8/0234 20130101;
H01M 8/04858 20130101; H01M 4/92 20130101; Y02E 60/50 20130101;
H01M 4/8663 20130101; H01M 8/16 20130101; H01M 8/1018 20130101;
H01M 8/04089 20130101; H01M 8/04201 20130101 |
International
Class: |
H01M 8/16 20060101
H01M008/16; H01M 8/04858 20060101 H01M008/04858; H01M 8/04082
20060101 H01M008/04082; H01M 8/1018 20060101 H01M008/1018; H01M
8/0234 20060101 H01M008/0234 |
Claims
1-122. (canceled)
123. A fuel cell comprising: a fuel comprising an anode-side
composition comprising biomass, a first polyoxometalate, water, and
a reaction product of the biomass and the first polyoxometalate; an
anode electrode in fluid communication with the fuel; a proton
exchange membrane, having a first side and a second side, the first
side communication with the anode electrode; a cathode electrode in
communication with the second side of the proton exchange membrane;
and a load circuit in electrical communication with the anode
electrode and cathode electrode.
124. The fuel cell of claim 123, wherein the first polyoxometalate
is selected from the group consisting of phosphomolybdic acid
(PMo.sub.12O.sub.40), phosphotungistic acid (PW.sub.12O.sub.40),
vanadium-substituted phosphomolybdic acid
(PMo.sub.9V.sub.3O.sub.40), addenda keggin type polyoxometalate
(H.sub.3PW.sub.11MoO.sub.40), and mixtures thereof.
125. The fuel cell of claim 123, wherein the anode-side composition
further comprises a contaminant comprising a metal ion, an
inorganic nonmetal species or organic containing the element
Nitrogen, Sulfur, Phosphorus, or a combination thereof.
126. The fuel cell of claim 123, wherein a portion of the fuel in
fluid communication with the anode electrode is at a temperature of
22.degree. C. to 150.degree. C.
127. The fuel cell of claim 123, wherein the anode electrode, the
cathode electrode, or both do not comprise a surface catalyst.
128. The fuel cell of claim 123, further comprising: an oxidizer
solution comprising a cathode-side composition in fluid
communication with the cathode electrode; an oxidizer gas mixing
tank in fluid communication with the oxidizer solution, and adapted
to receive an oxidizer gas, wherein the cathode-side composition
comprises a second polyoxometalate and water.
129. The fuel cell of claim 128, wherein the second polyoxometalate
is selected from the group consisting of phosphomolybdic acid
(PMo.sub.12O.sub.40), phosphotungistic acid (PW.sub.12O.sub.40),
vanadium-substituted phosphomolybdic acid
(PMo.sub.9V.sub.3O.sub.40), addenda keggin type polyoxometalate
(H.sub.3PW.sub.11MoO.sub.40), and mixtures thereof.
130. The fuel cell of claim 128, wherein the cathode-side
composition further comprises a neutralizer selected from the group
consisting of alkali metals, alkali earth elements, transition
metal cations, organic cations, and mixtures thereof, and the
cathode-side composition further comprises a reaction product of
the neutralizer and the second polyoxometalate.
131. The fuel cell of claim 130, wherein the reaction product of
the neutralizer and the second polyoxometalate comprises a
salt-substituted oxidizer.
132. The fuel cell of claim 128, wherein the second polyoxometalate
can be regenerated by oxygen gas.
133. The fuel cell of claim 128, wherein the anode-side composition
further comprises a contaminant comprising a metal ion, an
inorganic nonmetal species or organic containing the element
Nitrogen, Sulfur, Phosphorus, or a combination thereof.
134. The fuel cell of claim 128, wherein the anode electrode, the
cathode electrode, or both do not comprise a surface catalyst.
135. The fuel cell of claim 129, wherein the cathode-side
composition further comprises a neutralizer selected from the group
consisting of alkali metals, alkali earth elements, transition
metal cations, organic cations, and mixtures thereof; wherein the
cathode-side composition further comprises a reaction product of
the neutralizer and the second polyoxometalate; wherein the
anode-side composition further comprises a contaminant comprising a
metal ion, an inorganic nonmetal species or organic containing the
element Nitrogen, Sulfur, Phosphorus, or a combination thereof; and
wherein the anode electrode, the cathode electrode, or both do not
comprise a surface catalyst.
136. A method, comprising: reducing a fuel comprising biomass, a
first polyoxometalate, and water; pumping the fuel through a flow
plate in communication with an anode electrode of a fuel cell
comprising the anode electrode, a proton exchange membrane having a
first and a second side, the first side in communication with the
anode electrode, and the second side in communication with a
cathode electrode, and a load circuit; pumping an oxidizer through
a flow plate in communication with the cathode electrode of a fuel
cell; connecting a load to the load circuit.
137. The method of claim 136, wherein the first polyoxometalate is
selected from the group consisting of phosphomolybdic acid
(PMo.sub.12O.sub.40), phosphotungistic acid (PW.sub.12O.sub.40),
vanadium-substituted phosphomolybdic acid
(PMo.sub.9V.sub.3O.sub.40), addenda keggin type polyoxometalate
(H.sub.3PW.sub.11MoO.sub.40), and mixtures thereof.
138. The method of claim 136, wherein reducing the fuel comprises
heating the fuel to a temperature of 22.degree. C. to 350.degree.
C., illuminating the fuel with a light source, or both.
139. The method of claim 138, wherein the light source provides
light comprising a wavelength of 700 nm to 1000 nm.
140. The method of claim 136, wherein the oxidizer is a gas
comprising oxygen.
141. The method of claim 136, wherein the oxidizer is a solution
comprising a second polyoxometalate and water, and further
comprising the steps of: pumping the oxidizer through a gas mixing
tank; and pumping an oxidizing gas through the gas mixing tank.
142. The method of claim 136, wherein the fuel is pumped through
the flow plate in communication with the anode electrode at a
temperature of 22.degree. C. to 150.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application No. 61/928,760, filed Jan. 17, 2014, titled "Solar- or
Heat-Induced Direct Fuel Cell Using Polyoxometalate as
Photo-Catalyst and Charge Carrier," and to U.S. Provisional Patent
Application No. 62/051,443, filed Sep. 17, 2014, titled "High
Performance Low Temperature Direct Biomass Fuel Cells with Two
Liquid Regenerable Polyoxometalate Solutions," both of which are
incorporated herein by reference in their entirety.
TECHNICAL FIELD
[0002] This disclosure relates to compositions comprising an
oxidizer, water, and optionally a neutralizer, and methods of
making and using the same. This disclosure also relates to
compositions comprising biomass, a biomass-oxidizer, water, and
optionally an accelerant, and methods of making and using the
same.
BACKGROUND
[0003] With the depletion of fossil energy and growing
environmental concerns, developing renewable energy sources becomes
more and more important. Today, fossil fuels still dominate the
energy market, accounting for over 80% of global energy
consumption. Producing electricity to power our world from
sustainable energy sources (e.g., solar energy and biomass) can
reduce the dependence on fossil fuels.
[0004] Fuel cells are one option for power generation with
high-energy yield and low environmental impact. Fuel cell
technologies include, for instance, solid oxide fuel cells (SOFCs),
microbial fuel cells (MFCs), and polymer exchange membrane fuel
cells (PEMFCs). However, those technologies have a number of
disadvantages. SOFCs can require very high working temperatures
(e.g., 500.degree. C. to 1000.degree. C.) to gassify biomass. MFCs
can work at low temperatures, but very low electric power output,
rigorous reaction conditions, and limited lifetime can seriously
hinder their applications. PEMFCs can require expensive surface
catalysts on the fuel cell anode that cannot withstand even trace
amounts of impurities. Therefore, the fuel purification process for
PEMFCs can add additional cost. Additionally, PEMFCs cannot be used
to convert biomass to electricity, because the carbon-to-carbon
(C--C) bonds in the biomass cannot be completely electro-oxidized
to CO.sub.2 at low temperatures, even with the expensive surface
catalyst. Accordingly, improved methods and apparatuses to, for
instance, produce electricity from sustainable energy sources are
desirable.
SUMMARY
[0005] Disclosed herein are a variety of compositions including,
but not limited to, (1) compositions comprising an oxidizer, water,
and optionally a neutralizer, and (2) compositions comprising
biomass, a biomass-oxidizer, water, and optionally a accelerant. In
some embodiments, the compositions comprising an oxidizer, water,
and optionally a neutralizer can be used on the cathode-side of a
fuel cell. In some embodiments, the compositions comprising
biomass, a biomass-oxidizer, water, and optionally an accelerant
can be used on the anode-side of a fuel cell. Fuel cells comprising
those compositions are also disclosed herein. Some of the
compositions disclosed herein can also be used to extract lipids
from algae, and compositions, methods, and apparatuses relating
thereto are also disclosed herein.
[0006] Disclosed herein is a cathode-side composition comprising an
oxidizer comprising a polyoxometalate (POM) and water. In some
embodiments, the polyoxometalate is selected from the group
consisting of phosphomolybdic acid (PMo.sub.12O.sub.40),
phosphotungistic acid (PW.sub.12O.sub.40), vanadium-substituted
phosphomolybdic acid (PMo.sub.9V.sub.3O.sub.40), addenda keggin
type polyoxometalate (H.sub.3PW.sub.11MoO.sub.40), and mixtures
thereof. The cathode-side compositions can comprise an oxidizer, a
neutralizer, water, and a reaction product of the oxidizer and the
neutralizer. In some embodiments, the neutralizer is selected from
the group consisting of alkali metals, alkali earth elements,
transition metal cations, organic cations, and mixtures thereof. In
some embodiments, the composition comprises two moles or greater
(e.g, 3 moles, 4 moles, 6 moles) of the neutralizer for each mole
of the oxidizer. Cathode-side compositions are disclosed wherein
the oxidizer is a polyoxometalate. In some embodiments, the
oxidizer is present in the composition in an amount of from 1% to
70% (e.g., 5% to 10%) by weight of the composition. In some
embodiments, the reaction product is a salt-substituted oxidizer.
In some embodiments, the water is present in the composition in an
amount of 1% to 99%, by weight of the composition. Methods of
making and using the cathode-side compositions are also disclosed
herein.
[0007] Also disclosed herein are anode-side compositions comprising
biomass, a biomass-oxidizer, water, and a reaction product of the
biomass and the biomass-oxidizer. In some embodiments, the biomass
comprises organic matter. In some embodiments, the organic matter
comprises wood, starch, lignin, cellulose, ascorbic acid, algae,
wheat, protein, yeast, animal product, or a combination thereof. In
some embodiments, the biomass has an average particle size of 15 nm
to 10 cm. In some embodiments, the biomass is present in the
composition in an amount of from 0.5% to 70% (e.g., 5% to 10%), by
weight of the composition. In some embodiments, the
biomass-oxidizer is adapted to oxidize the biomass when exposed to
heat, light, or a combination thereof. In some embodiments, the
biomass-oxidizer is adapted to oxidize the biomass at a faster rate
when exposed to heat. In some embodiments, the biomass-oxidizer is
adapted to oxidize the biomass at a faster rate when exposed to
light. In some embodiments, the biomass-oxidizer can be regenerated
by oxygen gas. In some embodiments, the biomass-oxidizer comprises
a polyoxometalate. In some embodiments, the biomass-oxidizer is a
polyoxometalate selected from the group consisting of
phosphomolybdic acid (PMo.sub.12O.sub.40), phosphotungistic acid
(PW.sub.12O.sub.40), vanadium-substituted phosphomolybdic acid
(PMo.sub.9V.sub.3O.sub.40), addenda keggin type polyoxometalate
(H.sub.3PW.sub.11MoO.sub.40), and mixtures thereof. The
biomass-oxidizer can comprise a metal ion, in some embodiments.
[0008] In some embodiments, the biomass-oxidizer is present in the
anode-side composition in an amount of 0.5% to 50% (e.g., 5% to
10%), by weight of the composition. In some embodiments, the
anode-side composition further comprises a contaminant. In some
embodiments, the contaminant comprises a metal ion, an inorganic
nonmetal species or organic containing the element Nitrogen,
Sulfur, or Phosphorus. In some embodiments, the anode-side
composition further comprising an accelerant. In some embodiments,
the accelerant is selected from the group consisting of Lewis
acids, Bronsted acids, Lewis bases, and mixtures thereof. In some
embodiments, the accelerant improves the reduction degree of the
biomass-oxidizer. In some embodiments, the accelerant comprises a
transition metal ion. In some embodiments, the accelerant is
present in the composition in an amount of 1 ppm to 2% (e.g., 0.5%
to 2%) by weight of the composition. In some embodiments, the water
is present in the anode-side composition in an amount of 1% to 99%
(e.g., 40% to 70%), by weight of the composition. Methods of making
and using the anode-side compositions are also disclosed
herein.
[0009] A fuel cell is disclosed, comprising a fuel comprising the
anode-side composition, an anode electrode in fluid communication
with the fuel, a proton exchange membrane, having a first side and
a second side, the first side communication with the anode
electrode a cathode electrode in communication with the second side
of the proton exchange membrane, and a load circuit in electrical
communication with the anode electrode and cathode electrode. In
some embodiments, the fuel comprises the anode-side composition. In
some embodiments, the fuel cell comprises an oxidizer solution
comprising the cathode-side compositions disclosed herein, in fluid
communication with the cathode electrode. In some embodiments, the
fuel cell comprises an oxidizer gas mixing tank in fluid
communication with the oxidizer solution, adapted to receive an
oxidizer gas.
[0010] In some embodiments, the portion of the fuel in fluid
communication with the anode electrode is at a temperature of
22.degree. C. to 150.degree. C. In some embodiments, the anode
electrode comprises a carbon felt or graphite material. In some
embodiments, the anode electrode comprises a plurality of layers of
a carbon felt or graphite material. In some embodiments, the anode
electrode does not comprise a surface catalyst. In some
embodiments, the anode electrode comprises a surface catalyst. In
some embodiments, the surface catalyst comprises a catalyst
selected from the group consisting of: noble metal ions, metal
oxides, and mixtures thereof. In some embodiments, the proton
exchange membrane is a material adapted to be permeable to protons,
and not to electrons. In some embodiments, the proton exchange
membrane is made of a sulfonated tetrafluoroethylene-based
fluoropolymer-copolymer. In some embodiments, the proton exchange
membrane comprises a sulfonated tetrafluoroethylene-based
fluoropolymer-copolymer having the molecular formula
C.sub.7HF.sub.13O.sub.5S.C.sub.2F.sub.4. In some embodiments, the
proton exchange membrane comprises a ceramic semipermeable
membrane. In some embodiments, the proton exchange membrane
comprises polybenzimidazole. In some embodiments, the proton
exchange membrane comprises phosphoric acid. In some embodiments,
the cathode electrode comprises a carbon felt or graphite material.
In some embodiments, the cathode electrode comprises a plurality of
layers of a carbon felt or graphite material. In some embodiments,
the cathode electrode does not contain a surface catalyst. In some
embodiments, the cathode electrode contains a surface catalyst. In
some embodiments, the surface catalyst is selected from the group
consisting of: noble metal ions, metal oxides, and mixtures
thereof. In some embodiments, the fuel cell further comprises a
gaseous oxidizer in communication with the cathode electrode. In
some embodiments, the oxidizer gas comprises air. In some
embodiments, the oxidizer gas comprises oxygen gas.
[0011] A first method of operating a fuel cell is disclosed, which
can comprise reducing a fuel comprising an anode-side composition,
pumping the fuel through a flow plate in communication with an
anode electrode of a fuel cell comprising the anode electrode, a
proton exchange membrane having a first and a second side, the
first side in communication with the anode electrode, and the
second side in communication with a cathode electrode, and a load
circuit, pumping an oxidizer gas through a flow plate in
communication with the cathode electrode, and connecting a load to
the load circuit.
[0012] A second method of operating a fuel cell is disclosed, which
can comprise reducing a fuel, pumping the fuel through a flow plate
in communication with an anode electrode of a fuel cell comprising
the anode electrode, a proton exchange membrane having a first and
a second side, the first side in communication with the anode
electrode, and the second side in communication with a cathode
electrode, and a load circuit, pumping an oxidizer solution
comprising a cathode-side composition through a flow plate in
communication with the cathode electrode of a fuel cell, pumping
the oxidizer solution through a gas mixing tank, pumping an
oxidizing gas through the gas mixing tank, and connecting a load to
the load circuit.
[0013] In some embodiments, the oxidizing gas comprises oxygen gas.
In some embodiments, the oxidizing gas comprises air. In some
embodiments, the reducing the fuel comprises heating the fuel. In
some embodiments, reducing the fuel comprises heating the fuel to a
temperature of 22.degree. C. to 350.degree. C. In some embodiments,
reducing the fuel comprises illuminating the fuel with a light
source. In some embodiments, the light source comprises an
artificial light source. In some embodiments, the light source
comprises the sun. In some embodiments, the light source provides 1
mW/cm.sup.2 to 100 mW/cm.sup.2 of light energy to the fuel. In some
embodiments, the light source provides light having a wavelength of
380 nm to 750 nm. In some embodiments, the light source provides
light having a wavelength of 510 nm to 720 nm. In some embodiments,
the fuel receives light having a wavelength of 10 nm to 380 nm. In
some embodiments, the fuel is pumped through the flow plate in
communication with the anode electrode at a temperature of
22.degree. C. to 150.degree. C. In some embodiments, the anode
electrode comprises a carbon felt or graphite material. In some
embodiments, the anode electrode comprises a plurality of layers of
a carbon felt or graphite material. In some embodiments, the anode
electrode does not contain a surface catalyst. In some embodiments,
the anode electrode contains a surface catalyst. In some
embodiments, the surface catalyst comprises a catalyst selected
from the group consisting of: noble metal ions, metal oxides, and
mixtures thereof. In some embodiments, the proton exchange membrane
comprises a material adapted to be permeable to protons, and not to
electrons. In some embodiments, the proton exchange membrane
comprises a sulfonated tetrafluoroethylene-based
fluoropolymer-copolymer. In some embodiments, the proton exchange
membrane comprises a sulfonated tetrafluoroethylene-based
fluoropolymer-copolymer having the molecular formula
C.sub.7HF.sub.13O.sub.5S.C.sub.2F.sub.4. In some embodiments, the
proton exchange membrane comprises a ceramic semipermeable
membrane. In some embodiments, the proton exchange membrane
comprises polybenzimidazole. In some embodiments, the proton
exchange membrane comprises phosphoric acid. In some embodiments,
the cathode electrode comprises a carbon felt or graphite material.
In some embodiments, the cathode electrode comprises a plurality of
layers of a carbon felt or graphite material. In some embodiments,
the cathode electrode does not contain a surface catalyst. In some
embodiments, the cathode electrode contains a surface catalyst. In
some embodiments, the surface catalyst is selected from the group
consisting of: noble metal ions, metal oxides, and mixtures
thereof.
[0014] The details of one or more embodiments are set forth in the
description below. Other features, objects, and advantages will be
apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF THE FIGURES
[0015] The following Figures depict one or more embodiments
disclosed herein, and are not necessarily drawn to scale.
[0016] FIG. 1 depicts a fuel cell in accordance with an embodiment
disclosed herein.
[0017] FIG. 2 depicts a fuel cell having a gaseous oxidizer in
accordance with an embodiment disclosed herein.
[0018] FIG. 3 depicts a fuel cell having a liquid oxidizer in
accordance with an embodiment disclosed herein.
[0019] FIG. 4 depicts a direct biomass fuel cell coupled with
biomass-POM-I solution anode tank and POM-II-oxygen cathode
tank.
[0020] FIG. 5 depicts an oxidation and reduction cycle in
accordance with an embodiment disclosed herein.
[0021] FIG. 6 depicts the FT-IR spectrum of native starch and
starch-H.sub.3PMo.sub.12O.sub.40 (PMo.sub.12) complex after light
irradiation.
[0022] FIG. 7 depicts molecular weight distributions of starches
with different reaction periods measured by gel permeation
chromatography (GPC).
[0023] FIG. 8 depicts .sup.1H NMR spectrum of final products in the
degradation of starch.
[0024] FIG. 9 depicts .sup.13C NMR spectrum of final products in
the degradation of starch.
[0025] FIG. 10 depicts an emission gas collection experiment
apparatus used for gas chromatography (GC) analysis.
[0026] FIG. 11 depicts .sup.31P NMR spectrum of reaction solution
after several repeated irradiation and discharge cycles.
[0027] FIG. 12 depicts voltage-current density and power-current
density plots with different polyoxometalates (POMs) used in a
solar-induced fuel cell in accordance with an embodiment disclosed
herein.
[0028] FIG. 13 depicts the electron transfer and pH changes of a
starch and PMo.sub.12 composition when exposed to light in a
temperature-controlled environment for eighty hours, followed by
discharge through a fuel cell for nine hours.
[0029] FIG. 14 depicts the electron transfer and pH changes of a
starch and PMo.sub.12 composition when heated to 95.degree. C. in a
dark environment for five hours, followed by discharge through a
fuel cell for twelve hours.
[0030] FIG. 15 depicts Faradic efficiency versus time curve for
light and heat degradation processes.
[0031] FIG. 16 depicts experimentally determined extinction
coefficients with different concentrations of phosphomolybdic blue
solution, including pure deionized water as a control.
[0032] FIG. 17 depicts an experimental apparatus for testing the
light-to-heat conversion efficiency of different concentrations of
phosphomolybdic blue solution, including pure deionized water as a
control.
[0033] FIG. 18 depicts the change in temperature over time of
different concentrations of phosphomolybdic blue solution,
including pure deionized water as a control.
[0034] FIG. 19 depicts the change in temperature over time of a
solution containing starch and PMo.sub.12, including pure deionized
water as a control.
[0035] FIG. 20 depicts a calibration curve for determining the
reduction degree of PMo.sub.12 based on absorbance of light with a
wavelength of about 700 nm.
[0036] FIG. 21 depicts the absorbance of a starch and PMo.sub.12
composition when exposed to light for various intervals.
[0037] FIG. 22 depicts the absorbance of a starch and PMo.sub.12
composition when exposed to heat for various intervals.
[0038] FIG. 23 depicts voltage-current density and power-current
density plots of several compositions used to power a fuel cell
with varying current levels, where the compositions contain starch
and a PMo.sub.12 that is exposed to heat or light, including a
first control composition containing no PMo.sub.12, and a second
control composition containing starch and PMo.sub.12 composition
that was not exposed to light or heat.
[0039] FIG. 24 depicts voltage-current density and power-current
density plots of a starch and PMo.sub.12 composition at varying
current levels, where the composition is used to power a fuel cell,
and is exposed to light for three cycles.
[0040] FIG. 25 depicts the current discharged by a composition of
starch and PMo.sub.12 when irradiated with light at 100 mW/cm.sup.2
and heated to 95.degree. C., and discharged across a load of 1.6
.OMEGA..
[0041] FIG. 26 depicts voltage-current density and power-current
density plots of several compositions used to power a fuel cell
with varying current levels, where the compositions contain
PMo.sub.12 and various types of biomasses.
[0042] FIG. 27 depicts voltage-current density and power-current
density plots of several compositions used to power a fuel cell
with varying current levels, where the compositions contain
PMo.sub.12, cellulose, and an accelerant, including a control with
no accelerant.
[0043] FIG. 28 depicts a comparison of .sup.31P NMR spectra of
H.sub.3PMo.sub.12O.sub.40, H.sub.3PW.sub.12O.sub.40 and synthesized
H.sub.3PW.sub.11MoO.sub.40.
[0044] FIG. 29 depicts a proposed reaction pathway in the
degradation of glucose with POM-I in a direct biomass fuel
cell.
[0045] FIG. 30 depicts a calibration curve for POM-I solution with
different reduction degrees.
[0046] FIG. 31 depicts the UV-Vis absorbance of glucose-POM-I
reaction solution during the thermal degradation process (diluted
to 50 mmol/L).
[0047] FIG. 32 depicts the number of electrons transferred over
time during the illumination reduction.
[0048] FIG. 33 depicts the number of electrons transferred over
time during thermal reduction.
[0049] FIG. 34 depicts the .sup.31P NMR spectrum of synthesized
POM-II.
[0050] FIG. 35 depicts the .sup.51V NMR spectrum of synthesized
POM-II.
[0051] FIG. 36 depicts the relationship of log r of oxygen
oxidation of POM-II solution on the reduction degree of oxygen
oxidation of different sodium substitute salts of POM-II, wherein r
is the rate of reaction calculated in mol e.sup.-1 l.sup.-1
h.sup.-1.
[0052] FIG. 37 depicts the relationship of log r of oxygen
oxidation of POM-II solution on the reduction degree of oxygen
oxidation of different concentration of 2Na substitute salts of
POM-II, wherein r is the rate of reaction calculated in mol
e.sup.-1 l.sup.-1 h.sup.-1.
[0053] FIG. 38 depicts the total organic carbon (TOC) analysis of
the anode electrolyte solution in repeated thermal
reduction-discharge cycles.
[0054] FIG. 39 depicts voltage-current density and power-current
density plots for glucose-POM-I reaction system with different
light irradiation time.
[0055] FIG. 40 depicts voltage-current density and power-current
density plots for a glucose-POM-I reaction system with different
reaction time at elevated temperature (100.degree. C.).
[0056] FIG. 41 depicts .sup.1H NMR (solvent D.sub.2O) of final
products in the degradation of glucose with POM-I.
[0057] FIG. 42 depicts .sup.13C NMR spectrum (solvent D.sub.2O) of
final products in the degradation of glucose with POM-I.
[0058] FIG. 43 depicts Faradic efficiency versus time curve in a
direct biomass fuel cell at room temperature using preheated
glucose-POM-I solution as anode electrolyte.
[0059] FIG. 44 depicts voltage-current density and power-current
density plots for different biomasses at 80.degree. C.
[0060] FIG. 45 depicts the colors of different electrolyte
solutions used in the direct biomass fuel cell.
[0061] FIG. 46 depicts the power density during continuous
operation of a direct biomass fuel cell at 80.degree. C. for 4
hours.
[0062] FIG. 47 depicts voltage-current density and power
density-current density of the biomass fuel cell at 80.degree. C.
using ascorbic acid as fuel.
[0063] FIG. 48 depicts redox potentials of POM-II (0.3 mol/l) and
glucose-POM-I (2 mol/l and 0.3 mol/l respectively) electrolyte as a
function of reduction degree.
[0064] FIG. 49 depicts cyclic voltammograms of initial POM-I
solution on graphite electrode with the scan rate 10 mV/s at room
temperature.
[0065] FIG. 50 depicts cyclic voltammograms of thermal reduced
glucose-POM-I solution (2 mol/L and 0.3 mol/L respectively) on
graphite electrode with the scan rate 10 mV/s at room
temperature.
[0066] FIG. 51 depicts the redox rates (corresponding to different
colors) of oxygen and 2 Na substituted POM-II solution with
different concentration and reduction degree.
[0067] FIG. 52 depicts a pathway of redox reactions in a fuel
cell.
[0068] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0069] Disclosed herein are a variety of compositions including,
but not limited to, (1) compositions comprising an oxidizer, water,
and optionally a neutralizer, and (2) compositions comprising
biomass, a biomass-oxidizer, water, and optionally an accelerant.
In some embodiments, the compositions comprising an oxidizer,
water, and optionally a neutralizer can be used on the cathode-side
of a fuel cell. These cathode-side compositions can, among other
things, allow a fuel cell to operate without a gas/liquid interface
at the cathode electrode, prevent waste products from flooding the
cathode-side of the proton exchange membrane, operate without a
precious metal catalyst at the cathode (although a precious metal
catalyst can be used), eliminate the need to monitor the moisture
level of the proton exchange membrane, resist catalyst poisoning
due to impurities in the cathode-side composition, or a combination
thereof. In some embodiments, the compositions comprising biomass,
a biomass-oxidizer, water, and optionally an accelerant can be used
on the anode-side of a fuel cell. These anode-side compositions
can, among other things, allow for direct conversion of a wide
variety of biomass materials (including polymeric biomasses), allow
for direct conversion of some synthetic materials, resist catalyst
poisoning due to impurities, operate with a contaminated or
unprocessed biomass, use light or heat to improve the efficiency of
a fuel cell (including solar power or waste heat), operate without
a precious metal catalyst at the anode electrode (although a
precious metal catalyst can be used), enable use with multiple
electrodes in series or a 3-D cathode in cathode, or a combination
thereof. Fuel cells comprising those compositions are also
disclosed herein.
Anode-Side Compositions
[0070] The anode-side compositions disclosed herein can comprise
biomass, a biomass-oxidizer, water, and a reaction product. The
anode-side compositions disclosed herein can further comprise an
accelerant.
Biomass
[0071] The anode-side compositions disclosed herein can comprise
biomass. The biomass can comprise any material that can degrade by
giving up a proton (H.sup.+) electron (e.sup.-) pair. In some
embodiments, biomass is biological material derived from living, or
recently living organisms. In some embodiments, the biomass is
synthetic. In some embodiments, the biomass comprises a naturally
derived material that has been chemically modified. In some
embodiments, the biomass comprises organic matter. The organic
matter can include, but is not limited to, sugars, starches, fats,
proteins, lignocellulosic biomass, carbohydrate polymers, aromatic
polymers, cellulose, carboxymethylcellulose, hemicellulose,
microcrystalline cellulose, lignin, ethanol, butanol,
dimethylfuran, gamma-Valerolactone, uronic acids, phenols,
phenylproponols, xylose, miscanthus, switchgrass, hemp, corn,
poplar, willow, sourghum, sugarcane, bamboo, eucalyptus, palm oil,
wheat, straw, food waste, industrial waste, wood products,
household waste, yard clippings, wood chips, tree materials,
allamanda, D-glucose, pectin, and combinations thereof.
[0072] The biomass can further comprise a contaminant. The
contaminant can be any material or impurity contained alongside or
within the biomass. In some embodiments, the contaminant comprises
sulfur and its compounds, phosphate and its compounds, CO, polymer
and materials that can absorb or deposit on the membrane. In some
embodiments, the contaminants can comprise materials that can
poison a noble metal catalyst, such as a platinum catalyst.
[0073] The biomass can be present in the composition in any amount
sufficient to undergo oxidation by a biomass-oxidizer. In some
embodiments, the biomass is present in the composition in an amount
of 0.5% or greater (e.g., 1% or greater, 5% or greater, 10% or
greater, 20% or greater, 30% or greater, 40% or greater, 50% or
greater, or 60% or greater), by weight of the composition. In some
embodiments, the biomass is present in the composition in an amount
of 70% or less (e.g., 60% or less, 50% or less, 40% or less, 30% or
less, 20% or less, 10% or less, 5% or less, or 1% or less), by
weight of the composition. In some embodiments, the biomass is
present in the composition in an amount of from 0.5% to 70% (e.g.,
0.5% to 6%, 0.5% to 50%, 0.5% to 40%, 0.5% to 30%, 0.5% to 20%,
0.5% to 10%, 0.5% to 5%, 5% to 70%, 10% to 70%, 20% to 70%, 30% to
70%, 40% to 70%, 50% to 70%, 60% to 70%, 0.5% to 10%, 10% to 20%,
20% to 30%, 30% to 40%, 40% to 50%, 50% to 60%, 60% to 70%, 0.5% to
20%, 10% to 30%, 20% to 40%, 30% to 50%, 40% to 60%, 50% to 70%,
0.5% to 30%, 10% to 40%, 20% to 50%, 30% to 60%, 40% to 70%, 0.5%
to 40%, 10% to 50%, 20% to 60%, 30% to 70%, 0.5% to 50%, 10% to
60%, 20% to 70%, 0.5% to 60%, 10% to 70%), by weight of the
composition.
[0074] The biomass can comprise particles that are, in some
embodiments, spherical, angular, platy (or hyperplaty), or a
combination thereof. The biomass particles can have a shape
selected for a variety of reasons. For instance, the biomass
particles' shape can be selected to facilitate the speed of
reaction with the biomass-oxidizer. The biomass particles' shape
can be selected, for instance, based on surface area, ease of
handling, availability, or a combination thereof. The biomass
particles' shape can be natural (e.g., derived by natural wind or
water erosion) or artificially derived (e.g., by manufacturing
aspects such as with particular grinding equipment and methods).
The biomass can have a shape factor of from to 1:1 to 140:1. The
shape factor is a measure of an average value (on a weight average
basis) of the ratio of mean particle diameter to particle thickness
for a population of particles of varying size and shape as measured
using the electrical conductivity method and apparatus described in
U.S. Pat. No. 5,128,606, which is incorporated by reference herein
in its entirety. In some embodiments, the shape factor of the
biomass particles is 1:1 or greater (e.g., 1.5:1 or greater, 2:1 or
greater, 2.5:1 or greater, 3:1 or greater, 3.5:1 or greater, 4:1 or
greater, 4.5:1 or greater, 5:1 or greater, 5.5:1 or greater, 6:1 or
greater, 7:1 or greater, 8:1 or greater, 9:1 or greater, 10:1 or
greater, 20:1 or greater, 30:1 or greater, 40:1 or greater, 50:1 or
greater, 60:1 or greater, 70:1 or greater, 80:1 or greater, 90:1 or
greater, 100:1 or greater, 110:1 or greater, 120:1 or greater, or
130:1 or greater). In some embodiments, the shape factor of the
biomass particles is 140:1 or less (e.g., 130:1 or less, 120:1 or
less, 110:1 or less, 100:1 or less, 90:1 or less, 80:1 or less,
70:1 or less, 60:1 or less, 50:1 or less, 40:1 or less, 30:1 or
less, 20:1 or less, 10:1 or less, 9:1 or less, 8:1 or less, 7:1 or
less, 6:1 or less, 5.5:1 or less, 5:1 or less, 4.5:1 or less, 4:1
or less, 3.5:1 or less, 3:1 or less, 2.5:1 or less, 2:1 or less, or
1.5:1 or less). In some embodiments, the shape factor of the
biomass particles is from 1:1 to 140:1 (e.g., 1:1 to 2:1, 2:1 to
3:1, 3:1 to 4:1, 4:1 to 5:1, 5:1 to 10:1, 10:1 to 30:1, 30:1 to
80:1, 80:1 to 110:1, 110:1 to 140:1, 1:1 to 20:1, 20:1 to 120:1, or
120:1 to 140:1).
[0075] The size of the biomass particles can be chosen for a
variety of reasons, including but not limited to cost, mechanical
properties, energy output, availability, or a combination thereof.
For instance, the biomass particles' size can be chosen to minimize
the amount of biomass needed or to speed the reaction with the
biomass-oxidizer. For example, in some embodiments, biomass
particles having a smaller average particle size react more quickly
with the biomass-oxidizer. In some embodiments, the average
particle size of the biomass particles is 15 nm or greater (e.g.,
25 nm or greater, 50 nm or greater, 100 nm or greater, 150 nm or
greater, 200 nm or greater, 250 nm or greater, 300 nm or greater,
350 nm or greater, 400 nm or greater, 450 nm or greater, 500 nm or
greater, 550 nm or greater, 600 nm or greater, 650 nm or greater,
700 nm or greater, 750 nm or greater, 800 nm or greater, 850 nm or
greater, 900 nm or greater, 950 nm or greater, 1 .mu.m or greater,
2 .mu.m or greater, 3 .mu.m or greater, 4 .mu.m or greater, 5 .mu.m
or greater, 6 .mu.m or greater, 7 .mu.m or greater, 8 .mu.m or
greater, 9 .mu.m or greater, 10 .mu.m or greater). In some
embodiments, the average particle size of the biomass particles is
10 .mu.m or less (e.g., 10 .mu.m or less, 9 .mu.m or less, 8 .mu.m
or less, 7 .mu.m or less, 6 .mu.m or less, 5 .mu.m or less, 4 .mu.m
or less, 3 .mu.m or less, 2 .mu.m or less, 1 .mu.m or less, 950 nm
or less, 900 nm or less, 850 nm or less, 800 nm or less, 750 nm or
less, 700 nm or less, 650 nm or less, 600 nm or less, 550 nm or
less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or
less, 300 nm or less, 250 nm or less, 200 nm or less, 150 nm or
less, 100 nm or less, 50 nm or less, 25 nm or less). In some
embodiments, the average particle size of the particles is from 15
nm to 10 .mu.m (e.g., 25 nm to 50 nm, 50 nm to 100 nm, 100 nm to
250 nm, 250 nm to 500 nm, 500 nm to 750 nm, 750 nm to 1 .mu.m, 1
.mu.m to 2.5 .mu.m, 2.5 .mu.m to 5 .mu.m, 5 .mu.m to 10 .mu.m, 25
nm to 100 nm, 100 nm to 500 nm, 500 nm to 1 .mu.m, 1 .mu.m to 5
.mu.m, 2.5 .mu.m to 10 .mu.m, 25 nm to 250 nm, 50 nm to 500 nm, 100
nm to 750 nm, 250 nm to 1 .mu.m, 500 nm to 2.5 .mu.m, 750 nm to 5
.mu.m, 1 .mu.m to 10 .mu.m, 25 nm to 500 nm, 50 nm to 750 nm, 100
nm to 1 .mu.m, 250 nm to 2.5 .mu.m, 500 nm to 5 .mu.m, 750 nm to 10
.mu.m, 25 nm to 750 nm, 50 nm to 1 .mu.m, 100 nm to 2.5 .mu.m, 250
nm to 5 .mu.m, 500 nm to 10 .mu.m, 25 nm to 2.5 .mu.m, 50 nm to 5
.mu.m, 100 nm to 10 .mu.m, 25 nm to 5 .mu.m, 50 nm to 10 .mu.m, 25
nm to 10 .mu.m). Average particle size is determined by light
scattering.
Biomass-Oxidizer
[0076] The anode-side compositions disclosed herein can comprise a
biomass-oxidizer. The biomass-oxidizer can be any material that can
separate protons and electrons from biomass. In some embodiments,
the biomass-oxidizer is a material that separates protons and
electrons from biomass to serve as fuel in the anode of a fuel
cell. In some embodiments, the biomass-oxidizer is water-soluble.
In some embodiments, the biomass-oxidizer can be regenerated or
reduced by oxygen gas. In some embodiments, the biomass-oxidizer
has a lower redox potential than oxygen gas. In some embodiments,
the biomass-oxidizer comprises a polyoxometalate.
[0077] Polyoxometalates (POMs) are inorganic metal-oxygen cluster
anions. The clusters contain symmetrical core assemblies of
MO.sub.n, where the M is a metal selected from the group of:
Molybdenum (Mo), Tungsten (W), Vanadium (V), Titanium (Ti),
Zirconium (Zr), Niobium (Nb), Manganese (Mn), Cobalt (Co), Copper
(Cu), Zinc (Zn), Iron (Fe), Nickel (Ni), Cerium (Ce), Chromium
(Cr), Silver (Ag), Gold (Au), Palladium (Pd), Platinum (Pt),
Ruthenium (Ru), Yttrium (Y), Erbium (Er), Europium (Eu), Lanthanum
(La), and Osmium (Os). The number of Oxygen atoms (n) can vary with
the oxidation state of the metal M. The POMs can also contain one
or a few heteroatoms X selected from the group of: Phosphorus (P),
Silicon (Si), Carbon (C), Arsenic (As), Chlorine (Cl), Gallium
(Ga), Germanium (Ge), Antimony (Sb), Tin (Sn), Iodine (I), Boron
(B), Aluminum (Al), Bromine (Br), Bismuth (Bi), Arsenic (As),
Sulfur (S), Oxygen (O), Selenium (Se), Indium (In), and Lead (Pb).
These groups of atoms can assemble themselves in to various shapes
such as Keggin-type POMs, having the overall formula
XM.sub.12O.sub.40, Wells-Dawson-type POMs, having the overall
formula X.sub.2M.sub.18O.sub.62, Dexter-Silverton-type POMs, having
the overall formula XM.sub.12O.sub.42, and Anderson-Evans type POMs
having the overall formula XM.sub.6O.sub.24. In some embodiments,
the POMs contain only metal-oxygen clusters having the same metal
M, and the same number of oxygen atoms n. In some embodiments, the
POMs contain heterogenous combinations of metal-oxygen clusters,
with different metals M, and different numbers of atoms n. As would
be understood by a person having ordinary skill in the art, POMs
may comprise other structures, combinations of metal-oxygen
clusters, and other heteroatoms. By way of example, and not
limitation, some POMs comprise phosphomolybdic acid
(PMo.sub.12O.sub.40), phosphotungistic acid (PW.sub.12O.sub.40),
vanadium-substituted phosphomolybdic acid
(PMo.sub.9V.sub.3O.sub.40), addenda Keggin-type POM
(H.sub.3PW.sub.11MoO.sub.40), or mixtures thereof.
[0078] In some embodiments, the biomass-oxidizer can comprise
simple metal ions, such as the redox pairs of transition metal
ions, main group metal ions and the metal complexes associated with
inorganic or organic ligands, redox pairs of ions or molecules such
as Fe.sup.3+/Fe.sup.2+, Cu.sup.2+/Cu.sup.+, and inorganic redox
pairs such as I.sub.2/I.sup.3-, TEMPO
(2,2,6,6-tetramethylpiperidinyloxy) and its reduced form.
[0079] The biomass-oxidizer can be purchased commercially or
prepared by any method known in the art. For instance,
phosphomolybidic acid (H.sub.3[PMo.sub.12O.sub.40]) may be
purchased from TCI America.RTM., or phosphotungstic acid
(H.sub.3[PW.sub.12O.sub.40]) may be purchased from Chem-impex
Int'l, Inc, each of which can be used as a biomass-oxidizer.
Addenda Keggin-type POM H.sub.3PW.sub.11MoO.sub.40 can be
synthesized by refluxing a solution of mixed phosphomolybdic acid
and phosphotungstic acid with the mole ratio of 1:11
(n(H.sub.3[PMo.sub.12O.sub.40]):
n(H.sub.3[PW.sub.12O.sub.40])=1:11) for 1 hour. Then water can then
be evaporated in air at 80.degree. C. until reaching the
concentration of 0.3 mol/L. High-vanadium Mo--V-phosphoric
heteropoly acid aqueous solutions with modified composition
H.sub.12P.sub.3Mo.sub.18V.sub.7O.sub.85 may be synthesized using
MoO.sub.3 (purchased commercially from Alfa Aesar), V.sub.2O.sub.5
(purchased commercially from Alfa Aesar) and H.sub.3PO.sub.4
(purchased commercially from Alfa Aesar). The synthesis process can
then comprise: producing a first solution by adding 0.079 mol
(14.32 g) V.sub.2O.sub.5 to 600 ml cooled DI water
(.about.4.degree. C.), then adding 90 ml H.sub.2O.sub.2 (purchased
commercially from Aldrich) with magnetic stirring and cooling by
ice. After dissolving V.sub.2O.sub.5, 0.02 mol (2.3 g) of
H.sub.3PO.sub.4 (85 wt %) can be added and the mixture can be
stirred at room temperature to decompose the extra H.sub.2O.sub.2
for 2 hours. Then, a second solution can be prepared by adding 0.81
mol (116.64 g) MoO.sub.3 and 0.095 mol (10.96 g) H.sub.3PO.sub.4
(85 wt %) to 1,000 ml DI water, and boiling. After the second
solution turns to yellow, 200 ml of the first can be added
gradually (200 ml for one time), and the suspension can be heated
to its boiling temperature. After all of the first solution is
added, the suspension can be until MoO.sub.3 dissolves completely
and is evaporated to 150 ml. The concentration of High-vanadium
Mo--V-phosphoric heteropoly acid obtained by that method, when
used, was 0.3 mol/L. Sodium salts of High-vanadium Mo--V-phosphoric
heteropoly acid can be synthesized by neutralization of the
heteropoly acid POM-II with sodium carbonate (commercially
available from Aldrich).
[0080] The biomass-oxidizer can be present in the composition in
any amount sufficient to cause the biomass to oxidize. In some
embodiments, the biomass-oxidizer is present in the composition in
an amount of 0.5% or greater (e.g., 1% or greater, 5% or greater,
10% or greater, 20% or greater, 30% or greater, 40% or greater, 50%
or greater, or 60% or greater), by weight of the composition. In
some embodiments, the biomass-oxidizer is present in the
composition in an amount of 50% or less (e.g., 40% or less, 30% or
less, 20% or less, 10% or less, 5% or less, or 1% or less), by
weight of the composition. In some embodiments, the
biomass-oxidizer is present in the composition in an amount of from
0.5% to 50% (e.g., 0.5% to 1%, 1% to 5%, 5% to 10%, 10% to 20%, 20%
to 30%, 30% to 40%, 40% to 50%, 50% to 60%, 60% to 65%, 0.5% to 5%,
1% to 10%, 5% to 20%, 10% to 30%, 20% to 40%, 30% to 50%, 40% to
60%, 50% to 65%, 0.5% to 10%, 1% to 20%, 5% to 30%, 10% to 40%, 20%
to 50%, 30% to 60%, 40% to 65%, 0.5% to 20%, 1% to 30%, 5% to 40%,
10% to 50%, 20% to 60%, 30% to 65%, 0.5% to 30%, 1% to 40%, 5% to
50%, 10% to 60%, 20% to 65%, 0.5% to 50%, 1% to 60%, 5% to 65%,
0.5% to 60%, 1% to 65%, 0.5% to 65%,), by weight of the
composition.
Water
[0081] The anode-side compositions disclosed herein can comprise
water. In some embodiments, water can be substituted by or included
with another solvent, including any solvent that will not be
oxidized by the biomass-oxidizer. In an embodiment, water can be
replaced by light CO.sub.2 as a solvent. In some embodiments, water
is present in the composition in an amount of 0.5% or greater
(e.g., 5% or greater, 10% or greater, 25% or greater, 33% or
greater, 50% or greater, 75% or greater, 90% or greater, 95% or
greater), by weight of the composition. In some embodiments, the
water is present in the composition in an amount of 99% or less
(e.g., 95% or less, 90% or less, 75% or less, 50% or less, 33% or
less, 25% or less, 10% or less, 5% or less), by weight of the
composition. In some embodiments, the water is present in the
composition in an amount of from 0.5% to 99% (e.g., 0.5% to 5%, 5%
to 10%, 10% to 25%, 25% to 33%, 33% to 50%, 50% to 75%, 75% to 90%,
90% to 95%, 95% to 99%, 0.5% to 10%, 5% to 25%, 10% to 33%, 25% to
50%, 33% to 75%, 50% to 90%, 75% to 95%, 90% to 99%, 0.5% to 25%,
5% to 33%, 10% to 50%, 25% to 75%, 33% to 90%, 50% to 95%, 75% to
99%, 0.5% to 33%, 5% to 50%, 10% to 75%, 25% to 90%, 33% to 95%,
50% to 99%, 0.5% to 50%, 5% to 75%, 10% to 90%, 25% to 95%, 33% to
99%, 0.5% to 90%, 5% to 95%, 10% to 99%, 0.5% to 95%, 5% to 99%),
by weight of the composition.
Accelerant
[0082] The anode-side compositions disclosed herein can further
comprise an accelerant. In some embodiments, the accelerant is
added to the composition to help cleave glycosidic bonds present in
many biomass materials, such as cellulose. In some embodiments, the
accelerant comprises a Lewis acid, Bronsted acid, Lewis base, or a
mixture thereof. The Lewis acid can include Sn.sup.4+, Fe.sup.3+
and Cu.sup.2+ etc. In some embodiments, the accelerant comprises
transition metal ions, main group metal ions and the metal
complexes associated with inorganic or organic ligands, redox pairs
of ions or molecules such as Fe.sup.3+/Fe.sup.2+,
Cu.sup.2+/Cu.sup.+, and inorganic redox pairs such as
I.sub.2/I.sub.3.sup.-, TEMPO (2,2,6,6-tetramethylpiperidinyloxy)
and its reduced form.
[0083] The accelerant can be provided in any amount to, for
instance, aid the solution in cleaving glycosidic bonds. In some
embodiments, the accelerant is present in the composition in an
amount of 100 ppm or greater (e.g., 250 ppm or greater, 500 ppm or
greater, 750 ppm or greater, 0.1% or greater, 0.5% or greater,
0.75% or greater, 1% or greater, 1.5% or greater), by weight of the
composition. In some embodiments, the accelerant is present in the
composition in an amount of 2% or less (e.g., 1.5% or less, 1% or
less, 0.75% or less, 0.5% or less, 0.1% or less, 750 ppm or less,
500 ppm or less, 250 ppm or less), by weight of the composition. In
some embodiments, the accelerant is present in the composition in
an amount of from 100 ppm to 2% (e.g., 100 ppm to 250 ppm, 250 ppm
to 500 ppm, 500 ppm to 750 ppm, 750 ppm to 0.1%, 0.1% to 0.5%, 0.5%
to 0.75%, 0.75% to 1%, 1% to 1.5%, 1.5% to 2%, 100 ppm to 500 ppm,
250 ppm to 750 ppm, 500 ppm to 0.1%, 750 ppm to 0.5%, 0.1% to
0.75%, 0.5% to 1%, 0.75% to 1.5%, 1% to 2%, 100 ppm to 750 ppm, 250
ppm to 0.1%, 500 ppm to 0.5%, 750 ppm to 0.75%, 0.1% to 1%, 0.5% to
1.5%, 0.75% to 2%, 100 ppm to 0.1%, 250 ppm to 0.5%, 500 ppm to
0.75%, 750 ppm to 1%, 0.1% to 1.5%, 0.5% to 2%, 100 ppm to 0.5%,
250 ppm to 0.75%, 500 ppm to 1%, 750 ppm to 1.5%, 0.1% to 2%, 100
ppm to 1%, 250 ppm to 1.5%, 500 ppm to 2%, 100 ppm to 1.5%, 250 ppm
to 2%, 100 ppm to 2%), by weight of the composition.
[0084] Accelerants can be purchased commercially or prepared by any
method known in the art. For example, Sn.sup.4+ can be added to the
composition by adding SnCl.sub.4 (such as is commercially available
from Alfa Aesar) to the composition. Fe.sup.3+ can be added to the
composition by adding Fe.sub.2(SO.sub.4).sub.3 (such as is
commercially available from Alfa Aesar) to the composition.
Cu.sup.2+ can be added to the composition by adding CuSO.sub.4
(such as is commercially available from Alfa Aesar) to the
composition.
Reaction Product
[0085] In the anode-side compositions disclosed herein, the biomass
and biomass-oxidant can combine to produce a reaction product. In
some embodiments, when the biomass and biomass-oxidant are
combined, the biomass-oxidant can oxidize the biomass by removing
an electron (e.sup.-) from an oxygen molecule of the biomass, and
bonding with a proton (H.sup.+) from the biomass. By this process,
the biomass-oxidant obtains an electron/proton pair that can be
used to power a fuel cell. At the same time, the biomass loses an
electron and a proton, which can cause the biomass to degrade.
Where the biomass comprises a polymer, this oxidation can cause the
bond between biomass monomers to break, which can cause polymers to
break down into oligomers or monomers. Thus, the reaction product
can further comprise reduced biomass-oxidant, and oxidized biomass.
Where the biomass is a polymer, the reaction product can comprise
biomass oligomers or monomers. In some embodiments, the biomass and
biomass-oxidant reaction product can cause the protonation of
water, resulting in an increased concentration of hydronium atoms.
This can cause the pH of the reaction product to increase.
[0086] In some embodiments, the oxidation of biomass by a
biomass-oxidant can be activated or enhanced by either heating,
exposure to light, or both. In some embodiments, the biomass and
biomass-oxidant do not form a reaction product until exposed to
heat or light. In some embodiments, the biomass and biomass-oxidant
can produce a reaction product at a rate that increases with heat
and/or light exposure. In some embodiments, the biomass and
biomass-oxidant can form a reaction product without exposure to
heat or light. In some embodiments, biomass and biomass-oxidant can
form a reaction product without exposure to heat or light, but the
biomass and biomass oxidant may produce a reaction product at an
increased rate with heat or light exposure.
[0087] In some embodiments, the reduced biomass-oxidizer may be
regenerated through oxidation. In some embodiments, this
regeneration can be caused by passing the biomass and
biomass-oxidant reaction product through the anode flow plate of a
fuel cell, where the cathode flow plate is provided with an
oxidizer. In some embodiments, the reduced biomass oxidizer in the
reaction product is itself oxidized. Thus, the reaction product can
further comprise the oxidized biomass, including oligomers or
monomers, and a non-reduced biomass oxidant. In some embodiments,
the oxidation of reduced biomass-oxidant reaction product can cause
the de-protonation of water, resulting in an increased
concentration of hydroxide atoms. This can cause the pH of the
reaction product to decrease.
[0088] In some embodiments, the non-reduced biomass-oxidant can
further oxidize the oxidized biomass, producing a further-oxidized
biomass, and a reduced biomass-oxidant. In some embodiments, the
reduced biomass oxidant can be repeatedly regenerated, as discussed
above, and repeatedly oxidize the biomass, including biomass
oligomers and monomers.
Method of Making the Anode-Side Composition
[0089] In some embodiments, the anode-side compositions can be
formed by combining a biomass and a biomass-oxidizer in water. In
some embodiments, the anode-side compositions can be formed by
further adding an accelerant. In some embodiments, the anode-side
composition can further be exposed to heat, or light, in sufficient
quantities for the biomass-oxidizer to oxidize the biomass and form
a reaction product. In some embodiments, the anode-side composition
can contain a reduced biomass-oxidizer as a reaction product, which
can be regenerated by adding a gas containing oxygen to the biomass
oxidizer. In some embodiments, a reduced biomass-oxidizer reaction
product can be regenerated by circulating the anode-side
composition through the anode-side of a fuel cell, where an oxidant
gas is provided to the cathode-side of the fuel cell.
Cathode-Side Compositions
[0090] The cathode-side compositions disclosed herein can comprise
an oxidizer, water, and optionally a neutralizer and a reaction
product of the oxidizer and neutralizer.
Oxidizer
[0091] The cathode-side compositions disclosed herein comprise an
oxidizer. The oxidizer can be any material that can accept an
electron from another material. The oxidizer can be any material
described above as a biomass-oxidizer. In some embodiments, the
oxidizer is the POM known as high-vanadium Mo--V-phosphoric
heteropoly acid (H.sub.12P.sub.3Mo.sub.18V.sub.7O.sub.85). When
used in fuel cells with the anode-side compositions disclosed
herein, the cathode-side composition can be selected to have a
lower redox potential than the anode-side composition.
[0092] The oxidizer can be present in the cathode-side composition
in any amount sufficient to reduce an anode-side composition, or
other material whose oxidation is desirable. In some embodiments,
the oxidizer is present in the composition in an amount of 0.5% or
greater (e.g., 1% or greater, 5% or greater, 10% or greater, 20% or
greater, 30% or greater, 40% or greater, 50% or greater, or 60% or
greater), by weight of the composition. In some embodiments, the
oxidizer is present in the composition in an amount of 50% or less
(e.g., 40% or less, 30% or less, 20% or less, 10% or less, 5% or
less, or 1% or less), by weight of the composition. In some
embodiments, the oxidizer is present in the composition in an
amount of from 0.5% to 50% (e.g., 0.5% to 1%, 1% to 5%, 5% to 10%,
10% to 20%, 20% to 30%, 30% to 40%, 40% to 50%, 50% to 60%, 60% to
65%, 0.5% to 5%, 1% to 10%, 5% to 20%, 10% to 30%, 20% to 40%, 30%
to 50%, 40% to 60%, 50% to 65%, 0.5% to 10%, 1% to 20%, 5% to 30%,
10% to 40%, 20% to 50%, 30% to 60%, 40% to 65%, 0.5% to 20%, 1% to
30%, 5% to 40%, 10% to 50%, 20% to 60%, 30% to 65%, 0.5% to 30%, 1%
to 40%, 5% to 50%, 10% to 60%, 20% to 65%, 0.5% to 50%, 1% to 60%,
5% to 65%, 0.5% to 60%, 1% to 65%, 0.5% to 65%,), by weight of the
composition.
Neutralizer
[0093] In some embodiments, the cathode-side compositions can
contain a neutralizer. In some embodiments, the neutralizer may
consist of any of: alkali metals, alkali earth elements, transition
metal cations, organic cations, and mixtures thereof. In some
embodiments, the redox reaction rate can increase with a decrease
in acidity of cathode-side compositions. In some embodiments, added
cations can bond with, and neutralize, free hydroxide (OH.sup.-)
ions, causing the pH to rise. This can be accomplished by adding
some neutralizer-containing compounds to the cathode-side
composition. By way of example, and not limitation, sodium ions
(Na.sup.+) can be added to the cathode-side composition by adding
sodium carbonate (NaCO.sub.2), which can react with the
cathode-side composition by releasing Na.sup.+ ions into the
composition, along with carbon dioxide gas. As would be recognized
by a person having ordinary skill in the art, neutralizers can be
added to the cathode-side composition by any method known in the
art, including adding neutralizers directly, or
neutralizer-containing compounds that release metal cations in
solution.
[0094] Neutralizers can be added, for instance, in any amount
sufficient to neutralize free hydroxide ions. In some embodiments,
the neutralizer can be present in the composition in a molar ratio
of 4:1 parts oxidizer to neutralizer or greater (e.g., 3:1 or
greater, 2:1 or greater, 1:1 or greater, 1:2 or greater, 1:3 or
greater, 1:4 or greater, 1:5 or greater, 1:7 or greater). In some
embodiments, the neutralizer can be present in the composition in a
molar ratio of 1:10 parts oxidizer to neutralizer (e.g., 1:7 or
less, 1:5 or less, 1:4 or less, 1:3 or less, 1:2 or less, 1:1 or
less, 2:1 or less, 3:1 or less), by weight of the composition. In
some embodiments, the neutralizer can be present in the composition
in a molar ratio of 4:1 to 1:10 parts oxidizer to neutralizer or
greater (e.g., 4:1 to 3:1, 3:1 to 2:1, 2:1 to 1:1, 1:1 to 1:2, 1:2
to 1:3, 1:3 to 1:4, 1:4 to 1:5, 1:5 to 1:7, 1:7 to 1:10, 4:1 to
2:1, 3:1 to 1:1, 2:1 to 1:2, 1:1 to 1:3, 1:2 to 1:4, 1:3 to 1:5,
1:4 to 1:7, 1:5 to 1:10, 4:1 to 1:1, 3:1 to 1:2, 2:1 to 1:3, 1:1 to
1:4, 1:2 to 1:5, 1:3 to 1:7, 1:4 to 1:10, 4:1 to 1:2, 3:1 to 1:3,
2:1 to 1:4, 1:1 to 1:5, 1:2 to 1:7, 1:3 to 1:10, 4:1 to 1:3, 3:1 to
1:4, 2:1 to 1:5, 1:1 to 1:7, 1:2 to 1:10, 4:1 to 1:5, 3:1 to 1:7,
2:1 to 1:10, 4:1 to 1:7, 3:1 to 1:10, 4:1 to 1:10).
Water
[0095] The cathode-side compositions disclosed herein can comprise
water. In some embodiments, water can be substituted by another
solvent, including any solvent that will not be oxidized by the
oxidizer. In an embodiment, water can be replaced by light CO.sub.2
as a solvent. In some embodiments, water is present in the
composition in an amount of 0.5% or greater (e.g., 5% or greater,
10% or greater, 25% or greater, 33% or greater, 50% or greater, 75%
or greater, 90% or greater, 95% or greater), by weight of the
composition. In some embodiments, the water is present in the
composition in an amount of 99% or less (e.g., 95% or less, 90% or
less, 75% or less, 50% or less, 33% or less, 25% or less, 10% or
less, 5% or less), by weight of the composition. In some
embodiments, the water is present in the composition in an amount
of from 0.5% to 99% (e.g., 0.5% to 5%, 5% to 10%, 10% to 25%, 25%
to 33%, 33% to 50%, 50% to 75%, 75% to 90%, 90% to 95%, 95% to 99%,
0.5% to 10%, 5% to 25%, 10% to 33%, 25% to 50%, 33% to 75%, 50% to
90%, 75% to 95%, 90% to 99%, 0.5% to 25%, 5% to 33%, 10% to 50%,
25% to 75%, 33% to 90%, 50% to 95%, 75% to 99%, 0.5% to 33%, 5% to
50%, 10% to 75%, 25% to 90%, 33% to 95%, 50% to 99%, 0.5% to 50%,
5% to 75%, 10% to 90%, 25% to 95%, 33% to 99%, 0.5% to 90%, 5% to
95%, 10% to 99%, 0.5% to 95%, 5% to 99%), by weight of the
composition.
Reaction Product
[0096] The cathode-side compositions disclosed herein can further
comprise a reaction product. In some embodiments, the oxidizer in
the cathode-side composition can reduce, forming a
reduced-oxidizer. In some embodiments, the reduced oxidizer can be
a waste product. By way of example, and not limitation, where the
oxidizer is oxygen, the reduced oxidizer can be water. In some
embodiments, the reduced oxidizer is a reduced catalyst, such as a
POM. In some embodiments, the reduced oxidizer can be regenerated
by adding an oxidant gas to the cathode-side composition, such as a
gas containing oxygen.
[0097] In some embodiments, a neutralizer can be added to the
cathode-side composition. In some embodiments, the neutralizers
neutralize hydroxide ions present in the cathode-side composition,
causing the pH of the cathode-side composition to increase. Thus,
in some embodiments, the cathode-side composition reaction product
further comprises neutralized hydroxide atoms. By way of example,
and not limitation, where sodium ions are added to the cathode-side
composition (Na.sup.+), sodium hydroxide (NaOH) can be formed by
the combination of sodium and hydroxide. As would be understood by
any person having ordinary skill in the art, other alkali-metal
compounds can be formed in a cathode-side reaction product,
including potassium hydroxide (KOH), and lithium hydroxide
(LiOH).
Method of Making the Cathode-Side Composition
[0098] In some embodiments, the cathode-side composition can be
made by adding an oxidant to water. In some embodiments, the
oxidant is a POM, such as phosphomolybdic acid
(PMo.sub.12O.sub.40), phosphotungistic acid (PW.sub.12O.sub.40),
vanadium-substituted phosphomolybdic acid
(PMo.sub.9V.sub.3O.sub.40), addenda keggin type POM
(H.sub.3PW.sub.11MoO.sub.40), or a mixture thereof. In some
embodiments, making the cathode-side composition can include adding
an oxidant and a neutralizer to water. In some embodiments, the
step of adding a neutralizer to water can include adding a compound
containing a neutralizer to water.
Methods of Using the Compositions Disclosed Herein
[0099] The compositions disclosed herein can be used in a variety
of applications including, but not limited to, fuel systems. Some
embodiments can comprise a fuel cell 100 as shown in FIG. 1 and
FIG. 2. A fuel cell 100 can comprise a fuel 102, an anode flow
plate 104, a proton exchange membrane 106, a cathode flow plate
108, and an oxidizer 110. In some fuel cells, the fuel 102 can be
pumped through the anode flow plate 104, where it comes into fluid
communication with one side of a proton exchange membrane 106. In
some fuel cells, an oxidizer 110, such as oxygen gas, can be pumped
into the cathode flow plate 108, where it comes into fluid
communication with the opposite side of the proton exchange
membrane 106. Where the fuel 102 has a higher reduction potential
than the oxidizer 110, the fuel can donate a proton (H.sup.+) 112
and an electron (e.sup.-) 114 to the oxidizer 110. In some
embodiments, the proton exchange membrane 106 can be more permeable
to protons 112 than to electrons 114. As a result, protons can more
freely pass through the proton exchange membrane 106, and some
electrons can be diverted through the load circuit 116, and can
generate a current. The proton exchange membrane can be made of a
sulfonated tetrafluoroethylene-based fluoropolymer-copolymer, such
as those with a molecular formula formula
C.sub.7HF.sub.13O.sub.5S.C.sub.2F.sub.4, and those sold as
NAFION.RTM., a trademark owned by E. I. Du Pont De Nemours And
Company Corp. of Delaware. The proton exchange membrane can be made
of a ceramic semipermeable membrane, polybenzimidazole, or
phosphoric acid. In some embodiments, the fuel 102 can be provided
to the anode flow plate 104, at a temperature of 22.degree. C. to
150.degree. C. Where a proton 112 and electron 114 have passed to
the cathode flow plate 108, the oxidizer 110 can be reduced, which
can produce a waste product 118. For example, where a gas
containing oxygen is used as the oxidizer 110, the proton 112 and
electron 114 can combine with oxygen gas to produce water vapor as
a waste product 118.
[0100] In some embodiments, the fuel 102 can be an anode-side
composition as described herein, comprising biomass and a
biomass-oxidizer. In some embodiments, the biomass-oxidizer can be
sensitive to heat 120 and/or light 106. Some biomass-oxidizers,
such as POMs, can oxidize biomass by removing a proton and electron
pair from a biomass when exposed to heat 120 or light 122. When the
biomass-oxidizer oxidizes biomass, the oxidizer reduces. Thus, when
the biomass-oxidizer can be pumped through the anode flow plate
104, the biomass oxidizer can donate a proton (H.sup.+) 112 and an
electron (e.sup.-) 114 to the oxidizer 110 through the proton
exchange membrane 106 and load circuit 116.
[0101] Some embodiments can comprise a fuel cell with a liquid
oxidant 200, as shown in FIG. 3. A fuel cell with a liquid oxidant
200 can further comprise a liquid oxidant 202, a means for
regenerating the liquid oxidant 204, a secondary oxidant 206, and
an oxidant pump 208. Rather than passing a gas through the cathode
flow plate 108, an oxidant pump 208 can pump the liquid oxidant 202
through the cathode flow plate 108. The liquid oxidant 202 can
comprise an anode-side composition as described herein. In some
embodiments, an oxidant catalyst can be regenerated. In an
embodiment, an oxidant catalyst can be regenerated by bubbling a
secondary oxidant 210, such as an oxygen-containing gas, through
the liquid oxidant 202 in an oxidant exchange tank 204. When the
liquid oxidant 202 can be regenerated by pumping a secondary
oxidant 210 through the liquid oxidant 204, a waste gas 212 can be
produced. Where the secondary oxidant can be an oxygen-containing
gas, the waste gas 212 can comprise carbon dioxide gas. This
process is also depicted in FIG. 4.
[0102] As described above, fuel cells can comprise at least four
components: an anode, an electrolyte, a load circuit, and a
cathode. At the anode, a reduction reaction generates an
electron-proton pair. The positively charged proton (H.sup.+) may
propagate through the electrolyte to the cathode. The electrolyte
is less permeable to electrons than to protons, forcing electrons
to travel through the load circuit. At the cathode, an oxidation
reaction occurs, wherein the proton, electron, and an oxidant are
combined into a waste product.
[0103] Some embodiments disclosed herein comprise a solar-induced
hybrid fuel cell that directly consumes natural polymeric biomass,
such as starch, lignin, cellulose, switchgrass or wood powders. In
some embodiments, the biomass is oxidized by POMs in the solution
under solar irradiation, and the reduced POM is oxidized by oxygen
through an external circuit, producing electricity. Embodiments
disclosed herein can have many advantages. First, a fuel cell that
combines photochemical and solar-thermal biomass degradation in a
single chemical process can be built, leading to high solar
conversion and effective biomass degradation. Second, embodiments
disclosed herein need not use expensive noble metals as anode
catalysts, because the fuel oxidation reactions are catalyzed by
POMs in the solution. Finally, some embodiments can be directly
powered by unpurified polymeric biomasses, which can significantly
reduce the fuel cell cost. In some embodiments, the power density
of the fuel cells disclosed herein can reach 1 W/cm.sup.2. In some
embodiments, the power density of the fuel cells disclosed herein
is up to 10,000 times greater than fuel cells currently on the
market.
No Precious Metal Electrode Required
[0104] In the fuel cells disclosed herein below, the catalytic
reactions are mediated by the biomass-oxidizer, and not on the
surface of an expensive and process-sensitive precious metal
electrode or catalyst. Most biomass fuels, and even some artificial
polymers and organic wastes, can be directly degraded by the fuel
cells disclosed herein to provide electricity without using a
precious metal catalyst. Contaminants, such as organic impurities
in crude biomass can also be oxidized as fuels, and inorganic
impurities will not poison the whole process because the
biomass-oxidizers disclosed herein can be robust and self-healing.
As a result, the fuels used in the disclosed fuel cells do not have
to be pure. This can significantly reduce the cost of current fuel
cell technology, and it widens the range of biomass fuels that can
be used for electric power production. In embodiments where a metal
catalyst is used, any type of surface catalyst can be used as is
known in the art, such as those made of noble metals (Gold,
Platinum, Iridium, Palladium, Osmium, Silver, Rhodium, and
Ruthenium), metal oxides, and mixtures thereof.
Methods of Using Compositions in Fuel Cells
[0105] By way of non-limiting illustration, examples of certain
embodiments of the present disclosure are given below. In some
embodiments, a fuel cell can be operated by reducing a fuel
comprising an anode-side composition, as described herein. In some
embodiments, a fuel cell can be operated by reducing a fuel other
than an anode-side composition, as described herein, where the fuel
has a higher redox potential than the oxidizer used. In some
embodiments, the fuel cell can comprise a proton exchange membrane
sandwiched between an anode flow plate, containing an anode, and a
cathode flow plate, containing a cathode. In some embodiments, the
anode and cathode are electrically connected through a load
circuit. In some embodiments, the method of operating the fuel cell
can comprise pumping the reduced fuel through the anode flow plate,
and connecting a load to the load circuit.
[0106] The method of operating the fuel cell can further comprise
heating the fuel. The method of operating the fuel cell can
comprise heating the fuel to a temperature of 22.degree. C. to
350.degree. C. The method of operating the fuel cell can comprise
illuminating the fuel with a light source. The method of operating
the fuel cell can comprise illuminating the fuel with an artificial
light source. The method of operating the fuel cell can comprise
illuminating the fuel with the sun.
[0107] The method of operating the fuel cell can comprise
illuminating the fuel with 1 mW/cm.sup.2 to 100 mW/cm.sup.2 of
light energy. The method of operating the fuel cell can comprise
using a light source that provides light with a wavelength of 380
nm to 750 nm, 510 nm to 720 nm, 10 nm to 380 nm, or any combination
thereof. The method of operating the fuel cell can comprise pumping
the fuel through the anode flow plate at a temperature of
22.degree. C. to 150.degree. C. The method of operating the fuel
cell can comprise using a fuel cell wherein the anode electrode
comprises one or a plurality of layers of a carbon felt or graphite
material. The method of operating the fuel cell can comprise using
a fuel cell wherein the anode electrode does not contain a surface
catalyst. The method of operating the fuel cell can comprise using
a fuel cell wherein the anode electrode contains a surface
catalyst, such as a noble metal ion, metal oxide, or a mixture
thereof.
[0108] In some embodiments, the fuel cell can further com further
comprise a gaseous oxidizer. In these embodiments, the method of
operating the fuel cell further comprises pumping an oxidizer gas
through the cathode flow plate. In some embodiments, the oxidizing
gas comprises oxygen gas. In some embodiments, the oxidizer gas
comprises air. In some embodiments, the fuel cell can further
comprise a liquid oxidizer, such as any of the cathode-side
compositions described above. In these embodiments, the method of
operating the fuel cell can further comprise pumping the
cathode-side composition through the cathode flow plate, and
connecting a load to the load circuit.
[0109] In some embodiments, the fuel cell operation methods may be
performed where the proton exchange membrane comprises a material
adapted to be permeable to protons, and not to electrons. In some
embodiments, the proton exchange membrane can comprise a sulfonated
tetrafluoroethylene-based fluoropolymer-copolymer, including those
with molecular formula C.sub.7HF.sub.13O.sub.5S.C.sub.2F.sub.4, and
those commercially available under the mark NAFION.RTM., such as
NAFION.RTM. 115 and 117. In some embodiments, the proton exchange
membrane can comprise a ceramic semipermeable membrane,
polybenzimidazole, phosphoric acid, or combinations thereof. In
some embodiments, the cathode electrode can comprise one or a
plurality of more a carbon felt or graphite material. In some
embodiments, the cathode electrode does not comprise a surface
catalyst. In some embodiments, the cathode electrode can comprise a
surface catalyst, such as those selected from the group consisting
of: noble metal ions, metal oxides, and mixtures thereof.
Examples & Test Methods
Starch-PMo.sub.12 Complexes
[0110] As described above, some anode-side compositions comprise
biomass such as starch and a biomass-oxidizer, such as POMs. POMs
can oxidize biomass when exposed to sunlight, separating protons
and electrons from biomass to serve as fuel in the anode of a fuel
cell. For example, PMo.sub.12, a POM, oxidizes biomass when exposed
to sunlight by reducing from Mo.sup.6+ to Mo.sup.5+. Mo.sup.5+ can
be oxidized back to Mo.sup.6+ by oxygen through a catalytic
electrochemical reaction, as illustrated in FIG. 5. Electron
transfer from organics to POM under light irradiation could result
in the formation of an intermolecular charge transfer complex as
described in Yamase, T. Photo- and Elecrochromism of
Polyoxometalates and Related Materials. Chemical Reviews 98,
307-326 (1998), the entire disclosure of which is incorporated
herein by reference. According to this mechanism, the
representative reaction in a starch-PMo.sub.12 solution is as shown
in equation (1).
##STR00001##
[0111] PMo.sub.12 has a well-known Keggin structure, consisting of
a central tetrahedral [PO.sub.4] surrounded by twelve [MoO.sub.6]
octahedrons, which are photo-sensitive. Under short wavelength
light irradiation, an O.fwdarw.Mo ligand-to-metal charge transfer
can occur, where the 2p electron in the oxygen of [MoO.sub.6] can
be excited to the empty d orbital of Mo, which can change the
electron configuration of Mo from d.sup.0 to d.sup.1, and can leave
a hole at an oxygen atom in the [MoO.sub.6] octahedron. This hole
can interact with one electron on the oxygen atom of a hydroxyl
group of starch. Simultaneously, the hydrogen atom of the hydroxyl
group can shift to the POM lattice, and interact with the d.sup.1
electron, a thermally activated delocalization within the polyanion
molecule. Thus, the intermolecular charge transfer (CT) complex can
be thus formed, leading to the separation of photo-excited
electrons and holes, stabilizing the reduced state of
PMo.sub.12.
[0112] In several experiments discussed herein, a formed
starch-PMo.sub.12 complex was separated from the reaction solution
and characterized by FT-IR, which provides evidence of the
interaction between starch and PMo.sub.12 (shown in FIG. 6).
TABLE-US-00001 Standard PMo.sub.12 Starch-PMo.sub.12 complex Peaks
(cm.sup.-1) (cm.sup.-1) .upsilon.(Mo--O.sub.c--Mo) 785 785
.upsilon.(Mo--O.sub.b--Mo) 869 878 .upsilon.(Mo.dbd.O.sub.d) 962
956 .upsilon.(P--O.sub.a) 1068 1054
[0113] Because light irradiation also heats the starch-PMo.sub.12
solution, the oxidation of biomass by POMs by light and heat can
happen simultaneously in the presence of starch. As a result, a POM
captures an electron and proton from starch, oxidizing and
degrading the starch to oligomers and glucose derivatives as shown
in equation (2). POMs can accept more than one electron per Keggin
unit, which means the reduction degree of the POMs may
increase.
##STR00002##
[0114] Although one Mo is reduced from Mo.sup.6+ to Mo.sup.5+ by
forming a starch-POM complex, the total charge of the polyanion
(--[HPMo.sup.VI.sub.11Mo.sup.VO.sub.40].sup.3-) will not change
because a proton is also transferred from starch to the POM complex
at the same time. Because the standard redox potential of oxygen is
higher than that of the reduced POM, the Mo.sup.5+ in the reduced
PMo.sub.12 can be oxidized at the anode by passing a proton through
a membrane, and an electron through an external circuit, to O.sub.2
molecules at the cathode. As a result, the reduced POM (Mo.sup.5+)
gives one electron to the carbon anode and simultaneously releases
a proton to the solution. The electron passes through the external
circuit and is captured by oxygen to form water at the cathode. At
the same time, the starch molecules associated with PMo.sub.12 are
released into solution. The net effect of the above reaction is
that Mo.sup.5+ is oxidized back to Mo.sup.6+ at the anode, and the
starch is oxidized through dehydrogenation by POM catalysis.
Finally, the proton diffuses to the cathode side through the proton
exchange membrane and combines with oxygen to form water. The
entire discharge process is represented by equations (3) and
(4),
##STR00003##
[0115] Starch, which acts as the electron and proton donor, can be
directly oxidized under light radiation or hydrolyzed to small
oligomers by the POM, and then continuously oxidized to a series of
glucose derivatives such as aldehyde, ketones, and acids, as shown
in equation (5):
##STR00004##
[0116] The direct oxidation of starch in the photochromic reaction
was confirmed by FT-IR (FIG. 6), and the degradation and further
oxidation of starch glucose derivatives was verified by gel
permeation chromatography (GPC) (FIG. 7) and .sup.1H, .sup.13C NMR
analysis (FIG. 8 and FIG. 9).
TABLE-US-00002 Sample M.sub.n (g/mol) a1 12475; 5216 a2 11878; 4611
a3 10481; 5323; 2874 a4 6823; 2844 b1 9117; 4017 b2 5759; 2642
[0117] Additionally, CO.sub.2 is recognized as the final product in
many photo-degradation reactions of organic compounds by POMs, and
the produced CO.sub.2 was actually detected during the operation of
the solar-induced hybrid fuel cell in this example. FIG. 10 depicts
the experimental apparatus 300, including the gas collection tube
124. As the charge carrier in this example, PMo.sub.12 is very
stable in a solution acidified by H.sub.3PO.sub.4, which was
verified during our repeated cycle test using P NMR analysis (FIG.
11).
TABLE-US-00003 Results Concentration (mol %) Oxygen 21.37 Nitrogen
77.98 Carbon monoxide 0.012 Carbon dioxide 0.628
[0118] The performance of solar-induced fuel cells may be
associated with the reduction degree and redox potential of POMs.
As described below, the power density gradually increased after
three repeated light irradiation-discharge cycles. Correspondingly,
the reduction degree of the POM increased from 1.23 to 2.4
electrons per Keggin unit after three repeated
illumination/discharge cycles. Without wishing to be bound to
theory, it is believed that the reason for the increase in
reduction degree is that low molecular weight oligomers and
oxidized derivatives (mainly aldehydes) were formed during the
photo-catalytic reaction, which have greater reduction power and
higher reactivity with the POM. Therefore, with repeated light
irradiation-discharge cycles, more electrons were captured by each
Keggin unit, but without major changes in their chemical
structures.
[0119] The power density of the cell may be affected by the redox
potential of the POMs. As the charge carrier, POM is first reduced
by oxidizing the biomass, and then the reduced POM is oxidized by
oxygen. If the standard redox potential of POM is high, it has
greater tendency to oxidize the biomass but lower tendency to be
oxidized by oxygen. In the experiments described below three types
of POMs (PMo.sub.12, [PW.sub.12O.sub.40].sup.3-, and
[PV.sub.3MO.sub.9O.sub.40].sup.6-) with different redox potentials
were used as the charge and proton carriers (FIG. 12).
Faradic Efficiency
[0120] Faradic efficiency is considered as one important part of
discharge efficiency. Faradic efficiency is defined as a ratio of
the actual discharge capacity to the total electron charge
transferred from the organics in the POM electrolyte solution.
Faradic efficiency (.epsilon..sub.F) can be calculated with by
equation (6):
F = Q Discharging Q POM = .intg. 0 t I t FmVC POM ( 6 )
##EQU00001##
where Q.sub.Discharging is the experimental charge quantity
calculated from the discharge current-time curve, and Q.sub.POM is
the maximum possible charge quantity released by reduced POM,
calculated by spectrophotometry. I is the electric current obtained
during the discharging process; n is number of electrons obtained
per unit of POM; c.sub.POM is the concentration of POM; V is the
volume of electrolyte solution; and F is the Faraday constant.
[0121] Electron transfer in the starch-PMo.sub.12 system with
photochromic or thermal degradation was previously investigated, as
shown in FIG. 13 curve-1 and FIG. 14 curve-1. Results show that the
total amounts of electrons stored in reduced PMo.sub.12 solution
are 0.412 mmol e.sup.-/mL and 0.525 mmol e.sup.-/mL during
photochromic and thermal degradation respectively, which is equal
to 1.23 and 2.13 electrons per Keggin unit for photochromic and
thermal degradation respectively.
[0122] In the experiments described below, experimental single-POM
fuel cells achieved a Faradic efficiency as high as 91% and 94% in
the discharge of starch-PMo.sub.12 system for photo reduction and
thermal reduction, respectively (FIG. 15).
Light Sensitivity and Heat Sensitivity
[0123] In a series of experiments, the light sensitivity and heat
sensitivity of the redox process of POM-starch solutions were
investigated. Molybdenum blue, created when PMo.sub.12 is reduced,
can strongly absorb visible to near infrared light (700 nm to 1000
nm). This is caused by the inter-valence charge transfer (IVCT)
transitions. The long wavelength light absorption leads to the
conversion of light energy to thermal energy, which raises the
solution temperature. An experiment was conducted to test this
effect. Three test tubes were prepared, one containing a solution
of 1 mmol/L PMo.sub.12, one containing a solution of 10 mmol/L
PMo.sub.12, and one containing deionized water. Each test tube was
10 mm in diameter, and 175 mm long. The experimental apparatus is
depicted in FIG. 16 The characteristic absorption of each was
measured with a spectrophotometer. FIG. 17 documents the results,
showing the larger extinction coefficient than deionized water, and
thus greater absorbance across all measured wavelengths. Next, all
three were placed under a 50 W SoLux.RTM. Solar Simulator, and
exposed to simulated sunlight with an energy density of 100
mW/cm.sup.2. The temperature of each was measured with a
thermocouple for 70 minutes. FIG. 18 documents the results, showing
that both PMo.sub.12 solutions reached a greater temperature than
deonized water.
[0124] As shown in FIG. 19, the temperature of the
starch-PMo.sub.12 reaction solution used in the following
experiments can reach up to 84.degree. C. under actual sunlight
illumination (clear sky, 28.degree. C., Atlanta, Ga., USA) for 90
min. This is 20.8% higher than the maximum temperature reached by
deionized water exposed to the same sunlight conditions. POMs are
known to harvest electrons and protons from organic matter by
heating without illumination. Therefore, the redox reactions
between starch and PMo.sub.12 can be further enhanced by
heating.
[0125] A series of experiments were conducted to test the light and
heat sensitivity of the starch-PMo.sub.12 solution, which are
described below. The first experiment tested the light sensitivity
of the starch-PMo.sub.12 solution by exposing a starch-PMo.sub.12
solution to simulated sunlight, while maintaining the solution at a
constant temperature. The second experiment tested the heat
sensitivity of the starch-PMo.sub.12 solution by heating a
starch-PMo.sub.12 solution to an elevated temperature in a dark
environment. The results suggest that the biomass-POM reaction
system could combine photochemical and thermal biomass degradation
in a single process, which means that the sunlight utilization
could be extended to the near-infrared band.
Monitoring Reaction Degree
[0126] In these experiments, the number of electrons transferred
from starch to PMo.sub.12 was measured by monitoring the absorption
of light at a particular wavelength. As the concentration of
Mo.sup.5+ in the starch-PMo.sub.12 reaction solution increases, the
absorption of 750 nm light increases linearly. To determine an
equation for this relationship, a solution containing 1 mmol/L of
PMo.sub.12, without any added biomass, was reduced by
electrochemical reduction treatment at 3V for a variety of time
intervals. For each sample that had been reduced for a given time
interval, the absorption of 750 nm light was measured with an
AGILENT TECHNOLOGIES.RTM. 8453 UV-Visible Spectrophotometer. To
determine the actual reduction degree of PMo.sub.12, the samples
were titrated with potassium permanganate solution. The resulting
absorptions and reduction degrees are plotted in FIG. 20. From this
data, the reduction degree can be determined from absorption using
the best-fit slope of the relationship between absorbance (in a.u.)
and electron concentration (in mmol/L) is given by the equation
y=4.08326x10-4+1.58874x (Adjusted r.sup.2 value of 0.99826), where
y is absorbance and x is electron concentration. To make the
measurements during the following experiments, a sample of the
experimental solution was taken, and diluted until the sample
contained only 1 mmol/L of PMo.sub.12. Once diluted, the sample was
analyzed with the Spectrophotometer, and the reduction degree
calculated.
Fuel Solution
[0127] For the fuel solution, a starch-PMo.sub.12 solution was
mixed, consisting of phosphomolybdic acid, potato starch, and
phosphoric acid. The phosphomolybdic acid
(H.sub.3[PMo.sub.12O.sub.40], PMo.sub.12) with an .alpha.-Keggin
structure was acquired from TCI America. Potato starch solution was
obtained by cooking starch suspension for 20 min at 95.degree. C.
to obtain a 4% by weight potato starch solution. The fuel solution
was then prepared by combining the PMo.sub.12 and potato starch
solution in water, where the solution had a PMo.sub.12
concentration of 0.3 mol/L, and a potato starch concentration of 15
g/L. The starting pH of the solution was then adjusted to 0.3 by
adding phosphoric acid (85% aqueous solution, from ALFA
AESAR.RTM.), resulting in a clear yellow solution.
Light Sensitivity Test
[0128] To test the light sensitivity of the redox reaction, the
starch-PMo.sub.12 solution was kept at a constant temperature of
25.degree. C. by a recirculating water bath (RM6 Lauda, Brinkmann
Instruments Service, Inc.). The solution was then exposed to
AM1.5-type simulated sunlight, provided by a 50 W SoLux Solar
Simulator for a period of time at a distance of 10 cm from the
solution surface. For this experiment, the starch-PMo.sub.12
solution we used was placed in a clear, transparent glass beaker,
with the top open to air. The starch-PMo.sub.12 solution gradually
changes color from the initial yellow to deep blue, which indicates
the reduction of PMo.sub.12. FIG. 21 shows the absorbance of the
solution as a function of wavelength at different irradiation
times, showing increased absorption as the solution changes color.
At regular intervals, a very small amount solution was taken out as
a sample for analysis of the concentration of reduced PMo.sub.12
and the pH of the solution. The results are plotted in FIG. 13, in
the curve labeled 1. It can be seen that the electron transfer rate
continuously increased during the light irradiation period. After
80 hours, 0.41 mmol electrons were transferred from starch to
PMo.sub.12 per mL solution, which equals 1.23 electrons obtained
per Keggin unit.
[0129] Under light irradiation, the oxidation of starch by
PMo.sub.12 degraded the starch into low molecular weight segments,
which can improve reaction kinetics in repeated experiments. This
is because POM is not only a strong photo-oxidizing agent but also
a strong Bronsted acid. Meanwhile, a slight increase in pH of the
reaction solution during this photo-redox period was observed as
shown in FIG. 13. The addition of electrons decreases the acidity
of the POM, and is accompanied by protonation. Therefore, POM acts
as an electron and proton carrier during the photo degradation of
starch.
Heat Sensitivity Test
[0130] In an experiment to test the heat sensitivity of the
starch-PMo.sub.12 solution, the mixture was heated and kept at
95.degree. C. for 6 hours without light irradiation. The
starch-PMo.sub.12 solution used to test the heating effect was
modified from the starch-PMo.sub.12 solution used in the simulated
sunlight test above. Here, the solution was prepared of 15 g/L
potato starch (prepared as above), and 0.25 mol/L PMo.sub.12. The
pH was adjusted to 0.65 by adding phosphoric acid. The transfer of
electrons and change in pH of the solution during the
thermal-reduction experiment are shown in FIG. 13, which suggest
that 0.525 mmol electrons were transferred from starch to
PMo.sub.12 per mL solution by thermal degradation alone (equal to
2.13 electrons per Keggin unit). The light absorbance of the
heat-reduced starch-PMo.sub.12 solution also increased, as shown in
FIG. 23. The pH value increased from 0.65 to 0.74. The results
suggest that the designed biomass-POM reaction system could combine
photochemical and thermal biomass degradation in a single process,
which means that the sunlight utilization could be extended to the
near-infrared band.
Fuel Cell Used--Experimental Methods
[0131] Following these experiments, the heat- and light-reacted
starch-PMo.sub.12 solutions were then used to generate electricity
in a fuel cell, shown in FIG. 2. The fuel cell used a
commercially-available membrane electrode assembly, purchased from
Fuelcells Etc., of College Station, Tex., US. The electrolyte used
was a membrane composed of NAFION.RTM. 117. The anode electrode
consisted of five layers of carbon cloth on one side of the
membrane. The cathode electrode consisted of five layers of carbon
cloth impregnated with 60% Pt/C catalyst, loaded at 5 mg/cm.sup.2.
The Pt/C catalyst consisted of crystals between 4.0-5.5 nm, and the
specific surface area of the crystals was about 60 m.sup.2/g. The
bipolar plates of the cell were made of high-density graphite
plates with a straight flow channel 2 mm wide, 2 mm deep, and 5 cm
long (a total active area of 1 cm.sup.2). The MEA was sandwiched
between two graphite flow-field plates, which were clamped between
two acrylic plastic end plates. Rubber gaskets were included on the
circumference of the graphite flow-field plates to prevent any
leakage. In the experiment, the starch-PMo.sub.12 solution reduced
to molybdenum blue was pumped through the anode reaction cell, and
oxygen was flowed through the cathode cell using a compressed
oxygen cylinder. The temperature of the liquid in the cell was
about 25.degree. C. (room temperature). The solution flow rate
through the anode graphite plate was 12 mL/min and the oxygen flow
rate through the cathode was 75 mL/min at 1 atm. A DS345 30 MHz
(Stanford Research Systems) and a 4200-SCS (Semiconductor
characterization system, Keithley Instruments Inc.) were used to
examine the I-V curves using the controlled potentiostatic
method.
Control--No Heat or POM
[0132] Four solutions were used to power the fuel cell: a pure
starch solution, an untreated starch-PMo.sub.12 and the heat- and
light-treated solutions prepared in the previous experiments. The
results of these runs are shown in FIG. 23. As a control, a pure
starch solution (2.5% by weight) was provided to the anode side of
the fuel cell, and oxygen supplied to the cathode side of the fuel
cell. The power provided by the fuel cell was very small because of
the unavailability of a catalyst to electro-oxidize the starch.
When PMo.sub.12 was added without sunlight irradiation, the power
output still did not improve because the redox reaction between
PMo.sub.12 and starch could not take place at room temperature
without light irradiation. PMo.sub.12 in its original oxidation
state generally cannot oxidize starch in the hybrid cell at room
temperature without irradiation.
Treated Samples
[0133] Next, the simulated-sunlight treated starch-PMo.sub.12
solution was used to fuel the fuel cell. FIG. 13, in the curve
labeled 2, shows the number of discharged electrons, calculated by
integrating the electric current output curve. The number of
electrons discharged on the electrode was 0.375 mmol electrons per
mL solution, which is close to the calculated number shown in curve
1. This indicates that the electrons stored in the reduced
PMo.sub.12 were almost completely transferred to the cathode via
the external circuit and captured by O.sub.2. After discharging,
the pH was almost recovered to the original value because the
oxidation of the reduced POM led to the release of protons from the
POM to the solution. Finally, the heat-treated starch-PMo.sub.12
solution was used to fuel the fuel cell. FIG. 13 shows the number
of discharged electrons, calculated by integrating the electric
current output curve.
Cycling Light Sensitivity
[0134] An experiment was conducted to test whether the
light-sensitivity of the reduced starch-PMo.sub.12 was repeatable.
After the photo-irradiated solution was fully discharged, the
solution contained excess unreacted starch and its various
derivatives, which was then exposed to simulated solar light
followed by discharging again. In each cycle, the discharged
fuel-PMo.sub.12 solution was exposed to AM-1.5 simulated sunlight
and kept at constant 25.degree. C. until use. The solution was then
pumped into the anode of the fuel cell to electrically discharge
for several hours over a load of 1.6.OMEGA. resistance until the
current fell below 0.1 mA. The photo-irradiation-discharge cycles
were repeated three times and the power outputs were measured, as
illustrated in FIG. 24. The output power density increased with the
number of repeated cycles. A power density of 0.65 mW/cm.sup.2 was
reached on the third cycle, even though no extra starch or
PMo.sub.12 was added. The increase in the power density may be due
to the decrease in the starch molecular weight during the repeated
tests. The low molecular weight species from oxidation and acid
hydrolysis reduced the solution viscosity and increased the
reaction rate with POM molecules, as compared to high molecular
weight starch.
[0135] Different from the pre-light irradiation or pre-heating
tests conducted above, a continuous experiment with in-situ light
irradiation while producing electricity was also conducted. In the
continuous experiments, the transparent glass vessel was placed
under irradiation of AM 1.5-type simulated sunlight and heated to
95.degree. C. during a continuous discharge experiment. The glass
(sodium lime glass) was 2 mm thick, with transmission >95% for
wavelengths from 320 to 1100 nm and transmission >80% for
wavelengths from 270 to 320 nm (air as blank sample, measured on
AGILENT TECHNOLOGIES.RTM. 8453 UV-Visible Spectrophotometer). The
reaction solution was placed under simulated sunlight irradiation
and heated while being discharged simultaneously. The cell worked
continuously for almost 20 hours at a steady current density up to
2.5 mA/cm.sup.2, as shown in FIG. 25. Both repeated cycle tests and
in-situ continuous experiments indicate that the POM catalyst can
be reused without further treatment.
Different Biomasses
[0136] An experiment was conducted to test a variety of biomasses
were used to fuel an exemplary fuel cell. Cellulose, lignin,
switchgrass, and poplar powder were all tested. Crystalline
cellulose was purchased from Alfa Aesar. The cellulose suspension
was homogenized for 40 min to form a small particle suspension in
the solution before used. Lignin was isolated from a commercial USA
softwood Kraft pulping liquor. Switchgrass was from Ceres, Inc.
(Thousand Oaks, Calif.), and poplar was provided by Michigan State
University. These samples were washed with DI water and then dried
at 45.degree. C. overnight. The dry samples were then milled in a
Wiley mill through a 0.8 mm screen, yielding the biomass powder
directly used in this example without any pretreatment. FIG. 26
shows the power density that was produced by cellulose, lignin,
switchgrass, and poplar powder. The power density of our
solar-induced hybrid fuel cell can reach 0.65 and 0.62 mW/cm.sup.2
when fueled by poplar and switchgrass powders, respectively. All
these materials are water insoluble, so they were particle
suspensions at the beginning, but the biomass particles were
degraded and dissolved in the reaction solution as time progressed.
The results illustrate that all these biomass materials can be
directly used as fuel in this solar-induced hybrid fuel cell with
POM as catalyst and charge carrier.
Metal Ions as Accelerants
[0137] A fifth experiment was conducted to examine the effects of
adding metal ions to the biomass solution. The power density
produced by crystalline cellulose was lower than that obtained from
starch solution under similar conditions, probably because of the
slow hydrolysis of cellulose crystals. As discussed above, some
metal ions, such as Sn.sup.4+, Fe.sup.3+ and Cu.sup.2+ etc., could
function as Lewis acids to help cleave glycosidic bonds in, among
other biomasses, cellulose. In these experiments, the reaction
solutions consisted of 0.25 mol/L PMo.sub.12 and 0.1 g biomass with
a total solution volume of 20 mL and pH 0.5. The solution was
irradiated by simulated sunlight (100 mW/cm.sup.2) and heated on a
hotplate up to 95.degree. C. and kept for 6 hours (photo-thermal
experiment). The discharge condition was the same as the
starch-PMo.sub.12 system. To improve the reduction degree of
PMo.sub.12 in cellulose-PMo.sub.12 reaction system, some metal
salts as Lewis acids were added. The Lewis acids used in this
example include SnCl.sub.4 (Alfa Aesar, 0.188 mol/L) and
Fe.sup.3+-Cu.sup.2+ (Fe.sub.2(SO.sub.4).sub.3, Alfa Aesar, 0.15
mol/L; CuSO.sub.4, Alfa Aesar, 0.15 mol/L). Consequently, as shown
in FIG. 27, when these promoters were used in this system, the
power density increased, even up to 0.72 mW/cm.sup.2
(Cu.sup.2+-Fe.sup.3+ as promoters for PMo.sub.12), which is almost
100 times higher than that of cellulose-based microbial fuel cells
reported in literature.
POM-I Preparation and Reduction Rate Experiment.
[0138] To investigate the functional mechanisms of a two-POM fuel
cell, a series of experiments were conducted. A POM-I
polyoxometalate, having the formula H.sub.3PW.sub.11MoO.sub.40, was
synthesized by refluxing a solution of mixed phosphomolybdic acid
(H.sub.3[PMo.sub.12O.sub.40]) and phosphotungstic acid
(H.sub.3[PW.sub.12O.sub.40]) with a mole ratio of 1:11 for 1 hour.
Then, water was evaporated in air at 80.degree. C. until the
concentration of acid in the solution reached 0.3 mol/L. The
structure of the synthesized POM-I was verified by .sup.32P NMR, as
shown in FIG. 28.
[0139] A set of experiments was designed to test the redox reaction
between biomasses and the prepared POM-I solution. Glucose was used
as a model compound in these experiments. A glucose-POM-I mixture
was prepared, with 0.3 mol/L POM-I, and 2 mol/L glucose. A proposed
reaction pathway is given in FIG. 29. As with the experiments
above, the reduction degree of POM-I was measured by
spectrophotometry. Here, reduction degree (m) is represented by the
formula:
m = ( [ Mo 5 + ] + [ W 5 + ] ) [ POM - I ] ( 7 ) ##EQU00002##
[0140] To obtain a calibration curve, correlating reduction degree
to absorbance, pure POM-I solution at a concentration of 50 mmol/L,
without glucose, was reduced by electrochemical reduction at 3V for
a variety of time intervals. For each time interval, the absorbance
was measured with an Agilent Technologies 8453 UV-Visible
Spectrophotometer, and the reduction degree determined by titration
with potassium permanganate solution. The results are plotted in
FIG. 30, and reveal a calibration curve of y=2.551x-0.129, where X
is reduction degree, and Y is absorbance (in a.u.).
[0141] To test the reduction of the glucose-POM-I solution by
illumination, a 25 ml sample was placed in a glass vessel and
illuminated with AM 1.5-type simulated sunlight from a 50 W SoLux
Solar Simulator for 8 hours at a distance of 10 cm from the reactor
surface. The color of the solution gradually turned from yellow to
purple as the POM-I was reduced, increasing the absorbance of the
solution, as shown in FIG. 31. At various time intervals, a sample
of the reducing solution was taken, diluted to 50 mmol/L of POM-I,
and analyzed with the photospectrometer. The results of each of
these measurements is shown in FIG. 32.
[0142] To test the reduction of the glucose-POM-I solution by
heating, a 25 ml sample was placed in a glass vessel and heated to
100.degree. C. in the dark for 90 minutes. Samples were taken at
similar intervals and the same method as the illumination
experiment. The results of these measurements is shown in FIG.
33.
POM-II Formulation and Oxidation Experiment
[0143] A POM-II polyoxometalate, having the formula
H.sub.12P.sub.3Mo.sub.18V.sub.7O.sub.85, was synthesized by the
process described in V. F. Odyakov et al., Applied Catalysis A:
General 342, 126-130 (2008), the entirety of which is hereby
incorporated by reference as if fully set forth herein. A first
solution was prepared by adding 0.079 mol (14.32 g) V.sub.2O.sub.5
to 600 ml cooled deionized water (.about.4.degree. C.). 90 ml
H.sub.2O.sub.2 was added with magnetic stirring, and cooled by ice.
After the V.sub.2O.sub.5 was dissolved, 0.02 mol (2.3 g) of
H.sub.3PO.sub.4 (85% by weight) was added, and stirred at room
temperature for two hours, allowing the extra H.sub.2O.sub.2 to
decompose. A second solution was prepared by adding 0.81 mol
(116.64 g) MoO.sub.3 and 0.095 mol (10.96 g) H.sub.3PO.sub.4 (85%
by weight) to 1 L of boiling deionized water. After the second
solution turned yellow, the first solution was gradually added to
the second solution. This process was performed by pouring 200 ml
of the first solution into the second, then returning the solution
to a boil, and repeating until all of the first solution was
consumed. The combined solution was boiled until MoO.sub.3
dissolved completely, and then further evaporated to a volume of
150 ml. This resulted in a concentration of POM-II solution of 0.3
mol/L. The results of the synthesis were confirmed by .sup.31P and
.sup.51V NMR spectral analysis, shown in FIG. 34 and FIG. 35,
respectively.
[0144] Sodium salts of the POM-II solution were then synthesized by
neutralization of the heteropoly acid POM-II with sodium carbonate
(Aldrich). By controlling the mole ratio of POM-II and
Na.sub.2CO.sub.3, 2 Na, 3 Na, 4 Na, and 6 Na substitute POM-II were
prepared.
[0145] The concentration of synthesized POM-II solution was
determined by gravimetric analysis. 0.2 ml of solution was
transferred to a 10 ml beaker that had been dried at 120.degree. C.
to constant weight previously. Then the solution was dried at
120.degree. C. for constant weight.
[0146] The reduction degree of POM-II was determined by
potentiometric titration with 5 mmol/L potassium permanganate
solution (calibrated by standard sodium oxalate). The titration was
conducted in 1M phosphoric acid solution at room temperature using
an Ag/AgCl reference electrode (BASi) and a Pt wire electrode. The
reduction degree was given by the formula:
m = ( [ V 3 + ] ) [ POM - II ] ( 8 ) ##EQU00003##
[0147] An experiment was conducted to determine the oxygen
oxidation rate of POM-II. A 10 ml sample of POM-II was reduced by
electrochemical reduction treatment at 3V for varying times. An
initial reduction rate m.sub.o was determined. The solution was
then transferred to a glass flask with an airtight stopper, and
connected to a compressed oxygen cylinder. The flask was heated,
kept at a constant temperature of 80.degree. C., and vigorously
shaken by a Burrell wrist-action shaker. At regular intervals, 0.2
ml of solution was removed an analyzed to determine the reduction
degree. The amount of electrons transferred from reduced POM-II to
oxygen (A.sub.i) can be calculated by:
A.sub.i=(m.sub.i-m.sub.o)*c*v (9)
[0148] Where m.sub.i is the reduction degree at a given interval, c
is the concentration of POM-II solution, and v is the volume of the
POM-II solution. By differentiating the function A.sub.i=f(i) the
function r=f(m) can be obtained, where r is the reaction rate in
mol e.sup.-/L*h. This experiment was repeated for POM-II
concentrations of 0.3, 0.2, 0.1, and 0.05 mol/l POM-II. The results
of these experiments are given in FIG. 36. The experiment was
repeated for different sodium substituted salts of 2 Na, 3 Na, 4 Na
and 6 Na. The results of these experiments are given in FIG.
37.
Glucose Fuel Experiments
[0149] An experimental fuel cell was also constructed to test the
POM solutions. The fuel cell consisted of an anode flow plate and
electrode, cathode flow plate and electrode, proton exchange
membrane, and a load circuit. The flow plates had a serpentine flow
channel 2 mm wide, 10 mm deep, and 4 cm long (interface area of 1
cm.sup.2). The anode and cathode electrodes were constructed of a
graphite felt, purchased from Alfa Aesar. The electrode material
was pre-treated in an acid bath of concentrated sulphuric and
nitric acids in a 3:1 volumetric ratio at 50.degree. C. for 30
minutes. Following acid treatment, the electrodes were washed with
deionized water until the pH of the wash was neutral. The electrode
material was then dried at 80.degree. C., and cut into pieces 2 mm
wide and 10 mm long. These electrodes were placed on either side of
a MEA. The proton exchange membrane was made of NAFION.RTM. 115
(127 .mu.m thick). The membrane was pretreated in a boiling
solution of 1 mol/L H.sub.2SO.sub.4 (Aldrich) and 3% H.sub.2O.sub.2
(Aldrich) for 30 minutes, then washed and soaked in deionized
water.
[0150] The POM-I and biomass fuel were stored in a 35 ml glass
vessel connected to the anode flow plate of the fuel cell via a
PTFE tube and pump. When the pump was turned on, the POM-I and
biomass fuel mixture circulate through the anode flow plate at a
flow rate of about 30 ml/min, and a temperature of 80.degree.
C.
[0151] The POM-II solution was stored in a 35 ml glass vessel
connected to the cathode flow plate and an oxygen mixing tank via
PTFE tubing. The oxygen mixing tank consisted of a straight glass
column (1.5 cm diameter, 20 cm long) packed with carbon fibers. The
POM-II solution and oxygen gas (from a compressed oxygen cylinder)
were introduced into, and mixed in the column.
[0152] The oxygen mixing tank was maintained at a temperature of
80.degree. C. The POM-II solution was pumped through the oxygen
mixing tank at 30 ml/min, and the oxygen was introduced at a 15
ml/min flow rate at a pressure of 1 atm. The regenerated POM-II
solution leaving the oxygen mixing tank was then pumped into the
cathode flow plate of the fuel cell. As shown by Total Organic
Carbon analysis, the glucose broke down with repeated thermal
treatment, depicted in FIG. 38.
[0153] Both light- and heat-treated glucose-POM-I solutions were
tested in the experimental fuel cell. For each test run, a solution
consisting of 2 mol/L glucose and 0.3 mol/L POM-I was used. For
each trial, the anode electrolyte tank was heated to 100.degree. C.
The fuel solution was pumped through the anode flow plate at a rate
of about 10 ml/min, at a temperature of about 80.degree. C. The
POM-II solution consisted of 30 ml of water containing 0.25 mol/L
of 2 Na substituted POM-II salt solution. The POM-II solution was
pumped through the oxygen mixing tank at a rate of 15 ml/min, which
was maintained at a temperature of 80.degree. C., and 15 ml/min (at
1 atm) of oxygen gas was pumped through it.
[0154] POM can oxidize some organic materials not only by heating
but also by light irradiation. Besides simple heating, sunlight
induced glucose powered fuel cell with POM catalyst was also
studied. FIG. 39 shows that after irradiated with 8 h under
simulated sunlight (AM-1.5 simulated sunlight), the reduction
degree of POM-I increased up to 0.24 and the power density reaches
8.8 mW/cm.sup.2. However, when POM-I was mixed with glucose
solution without light irradiation, the power output was very low
as expected because the POM-I reduction could not occur without
light irradiation or thermal heat treatment.
[0155] Five trials were run with heat-treated glucose-POM-I, heated
to 100.degree. C. for 0, 30, 50, 70, and 90 minutes. The voltage
and power density at various current densities is shown in FIG. 40.
Four trials were run with light-treated glucose-POM-I, illuminated
for 0, 4, 6, and 8 hours. The voltage and power density at various
current densities is shown in FIG. 39. The final products of the
heat-treated glucose-POM-I were analyzed by .sup.1H and .sup.13C
NMR, the results of which are shown in FIG. 41 and FIG. 42,
respectively.
Faradic Efficiency Test
[0156] As one of important part of discharge efficiency, Faradic
efficiency was investigated during the discharging process of this
direct biomass fuel cell. In this experiment, Faradic efficiency
was measured by integrating the current discharging at room
temperature and comparing it with total electron charge transferred
from the biomass to the POM-I in anode solution. This measure
indicates the percentage of total electrons released from the
biomass in the anode that travels through the load circuit. The
results, given in FIG. 43, shows that the Faradic efficiency
reaches 92.4%.
[0157] To test the Faradic efficiency of the POM-I/POM-II fuel
cell, 3 ml of a solution consisting of 2 mol/L glucose and 0.3
mol/L POM-I was preheated to 100.degree. C. for 4 hours. The
reduction degree of the POM-I was then measured and recorded via
spectrophotometry. The number of electrons transferred from glucose
to POM-I could be calculated as m*c*v, where c is the
concentration, and v is the volume of POM-I. This pre-treated POM-I
solution was then placed in the anode electrolyte tank of the
experimental fuel cell. A sample of 20 ml of H-type POM-II solution
(0.3 mol/L) was placed in the cathode side of the fuel cell. Both
tanks were maintained at room temperature, and in the dark to
prevent additional reduction of the anode electrolyte. The
glucose-POM-I and POM-II solutions were circulated through the fuel
cell, which discharged across a load of 1.6.OMEGA. until the
current fell below 1 mA. The current was recorded every 1 s. From
this data, the Faradic Efficiency C.sub.F could be calculated
according to the following equation:
[0158] Where Q.sub.Discharging is the experimental charge quantity
calculated from the discharge current-time curve, and Q.sub.POM is
the maximum possible charge quantity released by 3 ml reduced
POM-I, calculated by spectrophotometry. I is the electric current
obtained during the discharging process, m is the reduction degree
of POM-I, C.sub.POM is the concentration of POM-I; V is the volume
of POM-I solution; and F is the Faraday constant. The results are
depicted in FIG. 43.
Various Biomass Fuel Tests
[0159] The performances of fuel cell powered by various biomasses
are shown in FIG. 44. Experimentally, 0.3 mol/L POM-I solution was
mixed with biomass in the anode tank and 0.3 mol/L POM-II solution
was filled in the cathode tank. Some biomasses, such as grass
powders, were particle suspensions in POM solution at the beginning
After preheating of POM-I in the anode tank at 100.degree. C. for 4
hours, the biomass was depolymerized to water-soluble fragments.
During this process, the color of POM-I solution changed from
yellow to deep purple POM-I solution was reduced (See FIG. 45). The
electrolyte solution was readily generating electric current in the
fuel cell when the external circuit was connected. As shown in FIG.
44, the power densities were 22 and 34 mW/cm.sup.2 respectively
when cellulose and starch were used as the fuels. Dry switchgrass
powder and freshly collected plants (bush allamanda) were also used
as the fuels. The power densities even reached 43 and 51
mW/cm.sup.2 respectively.
[0160] The continuous operation of a starch fueled cell was also
conducted under constant discharge current of 160 mA/cm.sup.2, as
shown in FIG. 46. The starch-POM-I solution was pre-heated to
80.degree. C. to ensure thermal reduction of POM-I before the
discharge test. For the cathode, POM-II was oxidatively regenerated
by mixing with oxygen in the cathode tank (details are given in
supplementary information). The cell worked continuously for about
4 hours under 80.degree. C. and the power density was stabilized at
c.a. 32 mW/cm.sup.2 (FIG. 46), which suggests both POM-I and
[0161] POM-II are regenerable under this experimental condition,
and the biomass fuel cell can continuously provide electricity by
directly consuming starch.
Experiment
[0162] As shown in FIG. 40, with glucose-POM-I system held in the
anode tank at 100.degree. C., the reduction degree kept increasing.
Correspondingly, the power density of the fuel cell output was
raised from 9.5 to 45 mW/cm.sup.2 with the increase of POM-I
reduction degree from 0.31 to 1.18 mole electron/mole POM after 90
min.
Ascorbic Acid Experiment
[0163] The ascorbic acid was used as fuel with extremely low
concentration, about 1 mg/mL. The ascorbic solution was mixed with
0.3 mol/L POM-I in anode fuel cell tank, After preheating ascorbic
acid at 80.degree. C. for half hour, the reduction degree of POM-I
reached 1.6. The performance of ascorbic fuel cell was measured
under the condition that the anode side was pumped with obtained
ascorbic-POM-I solution; and cathode side was pumped with 0.3 mol/L
POM-II with the flow rate 15 mL/min in both anode and cathode side.
The power density of ascorbic acid fueled cell was as high as 90
mW/cm.sup.2 (FIG. 47).
Experimental Results
[0164] The redox potential of POM-I solution and the entire fuel
cell performance are closely related to the reduction degree of
POM-I. During the redox reaction of POM-I and glucose, the formal
redox potential of POM-I was determined by connecting the graphite
working electrode with an Ag/AgCl reference electrode. As shown in
FIG. 48, fast redox potential drops were observed with the increase
of the reaction time between POM-I and glucose (anode electrolyte).
Specifically, redox potentials drop from 0.8 V (vs. NHE, on
graphite) to 0.35 V with the reduction degree increasing from 0 to
1.2. Cyclic volammograms were taken both of the initial, POM-I
solution, and a starch-POM-I solution (2 mol/L starch, 0.3 mol/L
POM-I) on a graphite electrode with a scan rate of 10 mV/s at room
temperature, the results of which are shown in FIG. 49, and FIG.
50.
[0165] For the cathode electrolyte, POM-II had a high initial redox
potential value of E (1.09 V vs. NHE, on graphite), which is shown
in FIG. 48. A graphical depiction of reduction degree as a function
of POM-II concentration is shown in FIG. 51. Unlike the anode
electrolyte POM-I, the formal redox potential of POM-II showed only
a small drop when the reduction degree of POM-II was increased. The
slow decrease of the reduction degree of POM-II is because this POM
composes 7 vanadium elements that act as "vanadium reservoir" to
maintain a relatively high redox potential during the discharge
process. Therefore, as the reduction degree of POM-I increases, the
voltage difference between anode POM-I and cathode POM-II raises as
does the fuel cell power output.
[0166] The stable performance during continuous operation of this
fuel cell is closely associated with all four steps shown in FIG.
52. For example, the discharging current is up to 200 mA/cm.sup.2
at the maximum point of depower density (shown in FIG. 44), which
means over 1 cm.sup.2 electrode, 7.46 mmol electrons were
transferred from anode to cathode within one hour. This suggests
that, to continuously produce 200 mA/cm.sup.2 current, the biomass
must transfer no less than 7.46 mmol electrons per hour to POM-I in
the anode tank (step 1), and reduced POM-II must transfer no less
than 7.46 mmol electrons per hour to oxygen in cathode tank (step
4) under the fuel cell conditions operated in the examples.
Advantages
[0167] The high-performance direct biomass fuel cell disclosed in
some embodiments herein can offer many advantages. For a
conventional fuel cell, the noble metal catalyst can be coated on
the membrane surface so the redox reaction rates on both cathode
and anode are limited by the project area of membrane. On the
contrary, regenerative POM solutions are used herein as catalyst
and mediators to transfer the charges in biomass fuel cell so no
metal electrode is needed. Furthermore, because the redox reactions
occur in polyoxymetalate solutions rather than on the electrode
surface, the redox reactions will not be limited by the membrane
area. Practically, multiple electrodes can be placed in either
anode or cathode tanks, which significantly increases the electrode
surface area. In a traditional fuel cell, the O.sub.2 molecules
must diffuse through a liquid thin layer to reach the surface of
catalyst, which limits the oxidation reaction rate on cathode. In
our fuel cell, the redox reactions occur in solution directly so
the gas-liquid-solid layer does not exist, which allows for a fast
redox reaction. Lastly, H.sup.+ ions diffusion is directly
conducted through anode and cathode liquids in our fuel cell, which
does not need to diffuse through the high resistance
liquid-solid-gas interface.
[0168] The direct biomass fuel cells herein incorporates the
photo-catalysis and thermal degradation of biomass in a single
process. In fact, most biomass fuels, mineral fuels, even some
artificial polymers and organic wastes can be directly degraded by
this POM to provide electricity at a low temperature
(80.about.100.degree. C.). The adoption of POM completely solves
the catalyst-poisoning problem because POMs are robust and
self-healing. As a result, the fuels used in the direct biomass
fuel cell do not require pre-purification treatment, which would
significantly reduce the fuel cost. In essence, this direct biomass
fuel cell can be a hybrid of fuel cell and redox flow battery,
which combines the advantages of both.
[0169] In summary, the present disclosure has demonstrated (in some
embodiments) a new non-noble metal fuel cell that can directly
consume natural biomass at low temperature and can provide a large
power-density close to the typical alcohol fuel cells. The
principle of using, for instance, a POM liquid and carbon as the
cathode can also be applied to other PEMFC systems to improve the
output power density and reduce the fuel cell cost. Therefore, the
POM direct biomass fuel cells disclosed in some embodiments herein
can represent a new pathway for biomass energy conversion.
[0170] The compositions and methods of the appended claims are not
limited in scope by the specific compositions and methods described
herein, which are intended as illustrations of a few aspects of the
claims and any compositions and methods that are functionally
equivalent are intended to fall within the scope of the claims.
Various modifications of the compositions and methods in addition
to those shown and described herein are intended to fall within the
scope of the appended claims. In particular, the presently
disclosed subject matter is described in the context of fuel cells.
The present disclosure, however, is not so limited, and can be
applicable in other contexts. For example and not limitation, some
embodiments may improve biomass processing techniques. Further,
while only certain representative compositions and method steps
disclosed herein are specifically described, other combinations of
the compositions and method steps also are intended to fall within
the scope of the appended claims, even if not specifically recited.
Thus, a combination of steps, elements, components, or constituents
may be explicitly mentioned herein or less, however, other
combinations of steps, elements, components, and constituents are
included, even though not explicitly stated. The term "comprising"
and variations thereof as used herein is used synonymously with the
term "including" and variations thereof and are open, non-limiting
terms. Although the terms "comprising" and "including" have been
used herein to describe various embodiments, the terms "consisting
essentially of" and "consisting of" can be used in place of
"comprising" and "including" to provide for more specific
embodiments of the invention and are also disclosed. Other than in
the examples, or where otherwise noted, all numbers expressing
quantities of ingredients, reaction conditions, and so forth used
in the specification and claims are to be understood at the very
least, and not as an attempt to limit the application of the
doctrine of equivalents to the scope of the claims, to be construed
in light of the number of significant digits and ordinary rounding
approaches.
* * * * *